Suppose that a person A happily entered a mutually romantic heterosexual relationship with another adult B and after suffering through three years of daily abuse, deliberate cruelty and elaborate attempts by B to make A feel jealous A separated themselves from B and swore off B's gender as a whole. Suppose that A is now an active homosexual and A and A's same gen partner C have decided to marry. Can A sue B for deliberate cruelty, abuse and emotional distress so severe that it turned A into a homosexual?
For cruelty and abuse, yes.
For sexual orientation change, you would need to prove a loss, i.e. that you are damaged or diminished as a result of that change, and your current partner might find that rather offensive! You would also need to prove your partner's culpability for that.
Those are very, very bold claims, which will require very, very bold proofs. Realistically I think your prospects are very, very poor. You have much better prospects on the ordinary abuse.
Further, the conversion claim will have terrible optics. It will gain national notoriety and will be the butt of jokes on late-night talk shows and "what is wrong with the world?" editorial columns. And I don't think I'm telling you anything you don't already know.
It will generate a great deal of negative publicity for you, will reflect badly on LGBT (which is something you ought to think about since you're part of it)... and you will be widely viewed as publicity-seeking opportunist and drama-maker, including by the judge and jury, and it will undercut your abuse claim. For that reason, the opponent's legal team will do everything possible to amplify that.
The long-term effects will be that you'll be "Oh yeah, that person", and people won't take you seriously for decades to come. It'll hurt your long term social and employment prospects.
It's the hard way to get your own page on Wikipedia.
If A is now happy with C and intending to marry, it would be hard to see how A's current same-gender preference is a wrong justifying money damages. Besides which it would be necessary to prove to the satisfaction of a judge or jury that B's actions has such an effect on A, which would be hard since I understand that current expert opinion does not support such a theory.
However, leaving aside the question of orientation "daily abuse, deliberate cruelty and elaborate attempts by B to make A feel jealous" might possibly constitute grounds for legal action. It would depend on the details of the "abuse". Physixcal assault, if proved, could be grounds for action. So can "Intentional Infliction of Emotional Distress". But ther would need to be something far beyond an ordinary dysfunctional romantic relationship. As lo this would be a matter of state law, so it would matter which state this was in. Unless the facts are rather extreme i do not see such an action being successful.
Anyone seriously considering such a legal action would do well to consult a competent lawyer.