First I'd like to apologize if I offended you in any way, I just naturally assume, when talking about relationships, that it's a boy and a girl, I know I shouldn't tho, so I'm sorry.
Now, this thing about him having countless other guys in his life, and that he acts the same way with them as he does with you, is a huge thing to keep in mind.
You're just another one in his list, one out of many, he does not value you in the same way you value him, there is no reciprocation, and no relationship can survive like this, at all. You need to move on, you deserve more than just being someone's option, a true relationship, with commitment, is about being someone's other half.
This paragraph, to me, was like looking into a mirror, so I'll try to help in any way I can, I think I can offer something here.
I know what it's like to be overly attached to our first love, my sadness truly became depression the day i got rejected by a girl that, to me, was everything, the first one i ever felt like i actually loved, and only one to this day, it's just so special when you feel it for the first time, it feels like it's meant to be, that this is what life is about, that you might not feel like this for anyone else ever again so we feel the need to make it work no matter what, almost out of desperation, and it's very easy to become codependent on that person, which is a terrible thing to be, and you dont deserve this.
I know it's much easier said than done, but please understand, it's clear that he doesn't value you in the way you deserve, and the more time you waste insisting on him, it's only gonna make you feel more regret when you give up, and it's also gonna be much harder to give up and move on, and you need to move on, there's plenty of fish in the sea, and certainly there's at least one out there that would appreciate this love you can give, and this loyalty and fidelity you have, in a way that this guy clearly never could.
Not saying that you should stop seeing him, you can still be friends, I'm still good friends with this girl, but just, dont insist on the romance, it's clear that your views of love, and his views, are not compatible.