Most of the stories I've read regarding the bisexual part end up with the same results. They end up coming out as gay at some point. This usually happens after they've formed an emotional attachment to a person. Similar to a regular hetro affair that starts out as purely sexual, the repeated contact helps to form a bond where love can grow. Most are familiar with situations where one spouse eventually leaves the other for the affair partner after they've fallen in love when the earlier intentions were for just thrills.
Scientific research shows that the human brain/body adapt and form to what we are feeding it to a grounding point. That explains so many of the stories of 20 plus years of a great marriage/sex suddenly taking a nose dive after one partner begins the same sex experimentation. You mentioned the last four of yours being rocky. Was it around that time that he began himself?
Sadly, it's rare they can stop and the stronger more addictive desire takes over and wins in the end. 
You answered your own question as why men only. That's his true sexual desire. His other desire is to love you and keep his straight life with promises not to act on his gay ones. But if that's the case then he wouldn't have acted on them in the first place and blame you for it. That's BS. 
It's a good thing your young because you still have a chance to find someone that will desire your love in all the ways you deserve.

Last edited by Scrupulous (December 26, 2018 1:47 pm)

My ex still identifies as bisexual.  Who knows.  Does it even matter?  It is not your fault that you are here. Gay hookup sites are the problem.  Being sexually confused is HIS problem.  Not yours.  

Don't let him decide what narrative drives you.  You have a rocky marriage because there is less intimacy than you need, then there is no therapy needed.  You cannot work on someone else's problem.  EVER.  Work on your anger. Work on yourself.  Get individual therapy if you need it, but the vast majority of people here find that there is a selfishness in these people and their situations - you need to figure out what YOU want.  Gah he's been experimenting on craigslist for years....Is that OK with you?  Is that what you fight about?   If so, then stop fighting as you will not win anything here.  Fidelity is not happening already....do you value that?  Honesty is not happening...Do you value that?    Go for what you value in life....find your happiness.  And if you have had 14 years of rocky marriage, then find a smoother path.  Divorce is hard, but there are good men out there.... and it isn't even about finding a replacement, but finding yourself and how you can be happy and fulfilled.  That is the challenge.