There are plenty of marriages that are loving and happy and do not involve sex. I get that this is not something you want, but let's just put that out there. Also, as soon as she said she didn't want sex, you just immediately stopped loving her? How deep/strong was that love to begin with if you can switch it off because of one aspect of a marriage? That is scary, to me, as a woman who has pain with sex. I have that fear that my husband would do the same thing you did.
As for the other person's comment about monogamy also meaning you fulfill all your partner's sexual desires, unless that was agreed to at the start, you can't go unilaterally amending the agreed upon contract/vows now and not expect repercussions. What if those sexual desires involved something the other person wasn't morally comfortable with, are you still obligated to help them fulfill them? I don't buy into that.
If you aren't going to leave her because you see it as quitting (which, in a sense, it is), and she is not willing/able to budge on sex-- seems you are at a stalemate. Also, if you don't trust women..... might make it hard to find anyone else to have a healthy relationship with anyways (not said in a judging way as I have trust issues with everyone ). Also, you could reframe that "not a quitter" into not quitting on your love or relationship. Otherwise, it seems you just want to feel like a martyr.
You mentioned that she was willing to do other aspects of sex, but that isn't enough for you and you don't like feeling like it is charity sex. Well, to me, that is a compromise on her part. She doesn't want the penetration (which, you guys have no idea how painful it can be when there are issues....but to me fair to you, she should talk to her doctor about it), but seemed willing to do other aspects. We get so hung up on penetration and orgasms, that we forget about all the other sexual things that can be done. Unless she says it is charity, perhaps you are reading into it or projecting. The fact that she was willing to do those things for you, to me, shows she is trying.
So, to answer your question: For various reasons throughout the years, I have at times not been able to have penetrative sex (or as much as my husband wanted). I fully expected him to stay monogamous (we weren't swinging during those periods) and to weather the storm with me. I was able and willing to provide him with oral and manual (though still not as much as he wanted because those hurt too). He watched a lot of porn and masturbated frequently (though, he watches porn like an addict, so that may not have had anything to do with me). I have thought about what I would do if I ever get to the point where I just can't do anything for a sexual release for the two of us. I might be willing to allow him to find someone else to have sex with in that case, but only if we weren't having sex or doing anything sexual at all anymore. I don't want to catch anything. I can't answer that question until it happens-- no one can. We can only say what we think/hope we would do. Anyone on here who says they would "for sure" do something is full of it. We don't know until we get there. There are a lot of emotions that go into saying you can't do something and allowing your partner to go elsewhere.