In my opinion, feminizing a cuckold husband or boyfriend has absolutely NOTHING to do with him being gay or even bisexual. It has to do with submission and psychological control of one person over another. In my case, for example, before my wife cuckolded me and then feminized me and turned me into a sissy slut, I had NO interest whatsoever in males or having anything to do with cocks. I loved pussy, and any porn I did look at was strictly heterosexual. I had suggested to my wife that she should have sex with other guys NOT because I wanted sex with them too but because I knew I was not even close to sexually satisfying her and she was becoming frustrated. It was my way of saving my marriage. Her willingness to do it was a total surprise to me, as I actually thought she would reject the idea. Then her desire to feminize me and turn me into a cocksucking sissy slut was not just a surprise, it was shocking to me, and I did resist at first. But, being basically submissive, I ended up submitting. In submitting, I did learn to accept it, then to like it as it was the only way I could get sexual relief, and then, after becoming addicted to it, I did learn to love and crave it.
Yes, there those who become feminized who actually WANT to be because of their gay curiosity or bisexual feelings, but that does not have to be the case in deciding whether to feminize a husband or boyfriend. It can happen regardless of that.