Hi there, I want to go back on two things.
First, I wanted to say that I really understands the poly thing. By which I mean when he says he'd feel better if you had other partners.
I've been in that boat, and I know the feeling of being pressured, of having your partner's pleasure depending solely on you (or so it felt at the time), especially as in my case he pretended not to masturbate for a while, which meant that I was not only his sole source of partnered sexual relief, but his sole source of sexual relief altogether! (As far as I knew. It turns out he was lying about it, which makes no sense to me as I was already having sexual problems at the time and had made it clear that it was one of the reasons).
The second thing is the masturbation thing. It's not a "lost opportunity to have sex with him". Masturbating and having sex are two very different things. And while it's possible to masturbate because you want to have sex but can't, the opposite is pretty rare. Even when my libido was at its lowest and I rarely ever had sex, I still masturbated for the most part. It was a completely different thing, something personal. With me, it doesn't matter how little or how much sex I get, I'm going to masturbate either way.
However, it is possible that he masturbates instead because it's "less of a hassle" for him.
Now that all leads me to a third thing. Right now there is some kind of vicious circle. If he's like me, the less he has sex, the less he wants sex, because the more he apprehends it. Even when I felt sexual, there was always a moment when I had to throw myself out there and say or show I wanted to have sex, and every time sounded so much like he was going "finally!" that I felt like the times we had sex, I was reproached the lack of sex MORE than if we didn't. He would also want it more after we had done it once than if we hadn't.
I also feared intimacy in other forms as I was afraid it would lead to sex. It happened that we snuggled, he wanted to have sex, I didn't, and he resented me for "teasing him" and "changing my mind" and things like that. Or I would start being affectionate and he would go "since I know
you don't want to have sex, stop that".
So I felt guilty when trying to be intimate without being sexual, which destroyed the connection we had in the first place, and made me want sex with him specifically less. And when I did want sex, his telling me he knew I didn't made me think "well, fine, since you know everything better than I do, you're right, I don't want to". I didn't want to have to contradict him, go out of my way to say I did want sex only to have him go "finally!!" and my libido to immediately drop down again, and then be blamed for changing my mind.
Anyway, I guess my point is that it's hard to get out of this cycle. It takes a lot of patience and rebuilding trust, and rebuilding your connection. It's like having to go through the first stage of a relationship or even the stage right before one, except now there is a past history that can get in the way.
And of course there is the possibility that it will never change at all. He's got a low sex drive and he's been abused, it's possible that he won't change. Are you fine with the idea of it staying that way forever? Because it might, and if you aren't, you might want to consider breaking it up. If it's a breaking-it-up offense.
As for having other partners, is he saying he wants other partners as well? You say it wouldn't be fair for him if you get to have them and he doesn't, does he agree with that reasoning or not? Because if he doesn't want or need other partners, for him that permission is useless, while your being allowed to have them might be priceless as it could be the thing that releases pressure for him. If, from his point of view, you refuse to have other partners, it might seem to him that you're voluntarily making him responsible for your lack of sex when you could have it elsewhere, and that
might not seem very fair to him at all.
So I would suggest you discuss the idea of your having other partners for sex and his not having other sexual partners, even if it's a momentary thing, and see how he reacts to it.
I would say that if he's relieved by that suggestion and enthusiastic about it, chances are his sex drive is never going to change, and it's not about you or the current relationship, it's just who he is.
If, however, he's very insistent of wanting other sexual partners, I would take it as a hint that it's a problem that's dependent on your relationship, that for whatever reasons he's not comfortable having sex with you more often but still wants sex with other partners.
In which case it's not necessarily a horrible thing. For instance, maybe he just has a dichotomy between sex and love. Maybe his sex drive is lower the more he's attached to someone. That's one possibility.
It could also be a bad thing, a sign that your specific relationship needs to be worked on. In which case I would work on it and tried to figure out what's wrong.
If that's what happens, I would suggest you take sex off the table completely until further notice. Don't initiate it, don't talk about it, do your best not to ever look like you miss it. Do whatever it takes to get your release in other ways. And focus on the relationship. If he's anything like me, he'll need to feel like you love him for him and not just for the sex. He needs to know you want a relationship with him for him, because you love him. The more you seem to miss sex, the more you seem to resent him for the lack of sex, the more he'll feel that's all he's worth to you, and the disconnect will grow bigger and bigger, and the issues will get worse as well.
I think that will be hard though. You said:
After trying to wait patiently for so long, I broke down crying. When he was confused about why I was upset, he told me he thought he had let me know it was ok for me to initiate sex again because we had had sex a few days before
(emphasis mine) which doesn't bode well. I mean, it seems to me like in that sentence you are saying a few days without sex is enough for you to cry over it, so I doubt you can go months without it and not show any signs of missing it. And unfortunately that might be what's needed.
So if that's what happens (and remember there are lots of ifs along the way), then staying together would probably cause both of you to be miserable. I know it's miserable being the less horny partner, it makes you feel emotionally drained, and constantly pressured without getting a rest, and it sounds like you're experiencing something very similar, that it adds up and doesn't reset when you do have sex, the time you had to wait before is still there, and you still feel a need to "make up for it" and it grows bigger and bigger constantly.
It's similar from the other side, by the way. Even having sex once doesn't reset all the apprehension and resentment and so on, there is a build-up that needs to be made up for as well.
In other words, in such a situation, you each grow a "debt" inside of you that the other partner "owes" you, and you're waiting patiently for it to get better, but it never does. And even if it does eventually, you both have so much to make up for that you might never be able to do it. (That's the kind of things I meant by the past history making it harder by the way).
Either way, I want to wish you good luck and I hope you can keep us posted so we know how things go.