It doesn't really matter if the OP is a gay male or a straight female.
The issue is one of disrespect.
OP, you are not being respected,
Your partner has libido fo others, but not you.
I'm not sure you actually wanted to agree to an "open" relationship, or if you felt it was a matter of going along with it, in order to please your partner, who quite frankly, is taking the piss....
It's horrible to finally admit to yourself, let alone others, that your relationship is a sham.... but it is, unfortunately.
If you can tolerate such behaviours simply to stay in this marriage, then so be it.
It sounds though, that you're very unhappy, and you wish your partner had libido for you....
Fact is, he hasn't.
If you want a partner for life, that is committed to YOU, then I think you probably need to end your so called marriage, and invest your love, your time, your respect, in a person who also wishes to show you the same....
I'm so sorry.
To have your live and commitment so disregarded is awful... please be kind to yourself, and not put up with anymore of this torture.