What could be the karmic punishment of a gay man who marries woman without telling her that he's gay, but fulfills her sexual and other needs and woman doesn't doubt it? Are there any scriptures that mention karmic punishments involving such fraudulent marriages?
Fraudulent marriages may distinctly fall under "PishAcha" marriage (sub demonic), which is the lowest category among all types of marriages. According to Manusmruti, chapter 3, among 8 types of marriages, 2 of them, viz. Asura & PishAcha -- should never by practiced.
- When (a man) by stealth seduces a girl who is sleeping, intoxicated, or disordered in intellect, that is the eighth, the most base and sinful rite of the Pisakas.
- But in these (Institutes of the sacred law) three of the five (last) are declared to be lawful and two unlawful; the Paisaka and the Asura (rites) must never be used.
If a gay person, succeeds in seducing a girl, because her intellect couldn't help her find the reality, then he may fall under extremely sinful marriage as above.
Karmik punishment could be hellish treatment in present life or afterlife.
Having said above, the case which you described doesn't seem that sinful to me. Because the gay man is satisfying the straight woman's physical needs.
According to Manusmriti:
A husband under no circumstances shall betray the trust, respect and honor of his wife, for another woman; for it will bring shame to himself, his family and wrath of God in afterlife.
So, as you can read Manusmriti law doesn't allow it and tells about consecutive punishment.
Scripture does not go into the the exact karmic consequences of any particular action. It only gives a general guidelines as to whether actions are sattvic, rajasic, or tamasic. The substance of your question is - what if one commits a life-long fraudulent act? Is not such a person being a liar in his actions to their family, society in general, as well as to the other person? Is not such a person being a hypocrite in order to gratify their own desires? Such an act is tamasic in nature. Krishna says in the Gita (Swami Nikhilananda translator):
14.16 The fruit of a good action is said to be good and clean; the fruit of rajas is pain, and the fruit of tamas is ignorance.
14.18 ...and those who are steeped in tamas, being weighted down by the tendencies of the lowest guna, go downward.
16.4 Ostentation, arrogance, and self-conceit; anger, rudeness, and ignorance--these belong to him who is born to the heritage of the demons.
16.7 Men of demonic nature know not what to do and what to refrain from doing. Purity in not in them, nor good conduct, nor truth.
16.8 They say: "The world is devoid of truth, without a moral basis, and without a God. It is brought about by the union of male and female, and lust alone is its cause: What else?
16.10 Giving themselves up to insatiable desires, full of hypocrisy, pride, and arrogance, they hold false views through delusion and act with impure resolve.
16.11-12 ...looking on the gratification of desire as their highest goal...given up wholly to lust and wrath, they strive by unjust means, to amass wealth for their satisfaction of their passions.
16.16 ...bewildered by many fancies, entangled in the meshes of delusion, addicted to the gratification of lust, they fall into a loathsome hell.
16.17 ...they ostentatiously perform sacrifices, which are so only in name, in utter disregard for precepts.
16.19 These cruel haters, these evil-doers, these vilest of men, I hurl always into the wombs of the demons in the cycle of births and deaths.
16.20 Having fallen into the wombs of demons and being deluded from birth to birth, they never attain Me, O son of Kunti, but go farther down to the lowest state.
16.21 Three are the gateways of this hell leading to the ruin of the self--lust, wrath, and greed. Therefore let man renounce these three.
Scripture tells us to control our passions, including lust--whether that lust is for a man or a woman.