The text and the marginal readings indicate the two chief constructions of this somewhat difficult verse. Other renderings are
(1) He who separateth himself from others seeks his own desire, and rushes forward against all wise counsel: a warning against self-will and the self-assertion which exults in differing from the received customs and opinions of mankind.
(2) he who separates himself (from the foolish, unlearned multitude) seeks his own desire (that which is worthy to be desired), and mingleth himself with all wisdom. So the Jewish commentators generally.
Between (1) blaming and (2) commending the life of isolation, the decision must be that (1) is most in harmony with the temper of the Book of Proverbs; but it is not strange that Pharisaism, in its very name, separating and self-exalting, should have adopted (2).

Through desire a man, having separated himself - The original is difficult and obscure. The Vulgate, Septuagint, and Arabic, read as follows: "He who wishes to break with his friend, and seeks occasions or pretenses shall at all times be worthy of blame."
My old MS. Bible translates, Occasioun seeketh that wil go awei fro a freend: at al tyme he schal ben wariable.
Coverdale thus: "Who so hath pleasure to sowe discorde, piketh a quarrel in every thinge."
Bible by Barker, 1615: "Fro the desire thereof he will separate himself to seeke it, and occupie himself in all wisdome." Which has in the margin the following note: "He that loveth wisdom will separate himself from all impediments, and give himself wholly to seek it."
The Hebrew: לתאוה יבקש נפרד בכל תושיה יתגלע lethaavah yebakkesh niphrad, bechol tushiyah yithgalla. The nearest translation to the words is perhaps the following: "He who is separated shall seek the desired thing, (i.e., the object of his desire), and shall intermeddle (mingle himself) with all realities or all essential knowledge." He finds that he can make little progress in the investigation of Divine and natural things, if he have much to do with secular or trifliing matters: he therefore separates himself as well from unprofitable pursuits as from frivolous company, and then enters into the spirit of his pursuit; is not satisfied with superficial observances, but examines the substance and essence, as far as possible, of those things which have been the objects of his desire. This appears to me the best meaning: the reader may judge for himself.

Through desire a man, having (a) separated himself, seeketh [and] intermeddleth with all wisdom.
(a) He who loves wisdom will separate himself from all impediments, and give himself wholly to seek it.

Through desire a man having separated himself, seeketh,.... Or, "a separated man seeketh desire" (g); his own desire, will, and pleasure. This is either to be understood in a good sense, of one that has a real and hearty desire after sound wisdom and knowledge, and seeks in the use of all proper means to attain it; and in order to which he separates himself from the world and the business of it, and retires to his study, and gives up himself to reading, meditation, and prayer; or goes abroad in search of it, as Aben Ezra: or of a vain man that affects singularity; and who, through a desire of gratifying that lust, separates himself, not only from God, as Jarchi interprets it, pursuing his evil imagination and the lust of his heart; and from his friends, as the Septuagint and Arabic versions; but from all men, like the Jews, who "please not God, and are contrary to all men"; so such a man sets himself to despise and contradict the sentiments and opinions of others, and to set up his own in opposition to them. This is true of the Pharisees among the Jews, who had their name from separating themselves from all others, having an high opinion of their own Wisdom and sanctify; and also of the Gnostics among the Christians, who boasted of their knowledge, and separated themselves from the Christian assemblies; and were sensual, not having the Spirit, being vainly puffed up with their fleshly mind;
and intermeddleth with all wisdom; the man who is desirous of being truly wise and knowing grasps at all wisdom, every branch of useful knowledge; would gladly learn something of every art and science worthy of regard; and he makes use of all means of improving himself therein; and covets the company and conversation of men of wisdom and knowledge, that he may attain to more; he intermingles himself with men of wisdom, as Aben Ezra interprets it, and walks and converses with them. Or if this is to be understood of a vain glorious person, the sense is, "he intermeddles" or "mingles himself with all business" (h), as it may be rendered; he thrusts himself into affairs that do not concern him, and will pass his judgment on things he has nothing to do with; or he monopolizes all knowledge to himself, and will not allow any other to have any share with him. Jarchi interprets this clause thus,
"among wise men his reproach shall be made manifest;''
and observes, that their Rabbins explain it of Lot separating from Abraham, following the desires of his heart: but R. Saadiah Gaon better interprets it of an apostate from religion; that objects to everything solid and substantial, in a wrangling and contentious manner; and "shows his teeth" (i) at it, as Schultens, from the use of the Arabic word, renders it.
(g) So the Targum. (h) "immiscet se omni negotio", Munster; "omnibus quae sunt immiscet se", Junius & Tremellius. (i) "Et in omne solidum dentes destringei", Schultens.

If we would get knowledge and grace, we must try all methods of improving ourselves.

(Proverbs. 18:1-24)
Through desire . . . seeketh--that is, seeks selfish gratification.
intermeddleth . . . wisdom--or, "rushes on" (Proverbs 17:14) against all wisdom, or what is valuable (Proverbs 2:7).

This series of proverbs now turns from the fool to the separatist:
The separatist seeketh after his own pleasure;
Against all that is beneficial he showeth his teeth.
The reflexive נפרד has here the same meaning as the Rabbinical פּרשׁ מן־הצּבּוּר, to separate oneself from the congregation, Aboth ii. 5; נפרד denotes a man who separates himself, for he follows his own counsel, Arab. mnfrd (mtfrrd) brâyh, or jḥys almḥḥl (seorsum ab aliis secedens). Instead of לתּאוה, Hitzig, after Jerome, adopts the emendation לתאנה, "after an occasion" (a pretext), and by נפרד thinks of one pushed aside, who, thrown into opposition, seeks to avenge himself. But his translation of 1b, "against all that is fortunate he gnasheth his teeth," shows how much the proverb is opposed to this interpretation. נפרד denotes one who willingly (Judges 4:11), and, indeed, obstinately withdraws himself. The construction of יבקּשׁ with ל (also Job 10:6) is explained by this, that the poet, giving prominence to the object, would set it forward: a pleasure (תאוה, as Arab. hawan, unstable and causeless direction of the mind to something, pleasure, freak, caprice), and nothing else, he goes after who has separated himself (Fl.); the effort of the separatist goes out after a pleasure, i.e., the enjoyment and realization of such; instead of seeking to conform himself to the law and ordinance of the community, he seeks to carry out a separate view, and to accomplish some darling plan: libidinem sectatur sui cerebri homo. With this 1b accords. תּוּשׁיּה (vid., at Proverbs 2:7) is concretely that which furthers and profits. Regarding התגּלּע, vid., at Proverbs 17:14. Thus putting his subjectivity in the room of the common weal, he shows his teeth, places himself in fanatical opposition against all that is useful and profitable in the principles and aims, the praxis of the community from which he separates himself. The figure is true to nature: the polemic of the schismatic and the sectary against the existing state of things, is for the most part measureless and hostile.

Desire - Thro' desire of wisdom, a man having separated himself from the company, and noise, and business of the world, seeketh and intermeddleth with all wisdom, uses all diligence, that he may search and find out all solid knowledge and true wisdom.