Besides the issue of their own happiness, whcih is totally valid, there is the issue of their spouses' happiness. Who would want to be married to a person who is suppressing their true orientation? I have never been with bisexual people but sure I can picture myself married to a truly bisexual man who also has male partners so as to satisfy both parts of his orientataion. Of course I would have no problem with that. But that stretches the conventional definition of marriage a bit. To stay in a conventional marriage with a man who suppresses his homosexual leanings must be depressing. And what for? There is no deficit of straight men, who are in the majority.