I'm gonna go through and try to sort this out...

I got great advice telling me to ask him if it was ok if I touched myself while we had sex, and he agreed! Which was fantastic.

Unless you're teasing and denying, this doesn't seem like something that should require anybody's permission.

it was a quickie and I didn't get off because we were in a rush.

That's a sign of a pretty selfish lover. Especially if it happens more often than not.

I always try to initiate it. But he pushes me away and gets mad because he says I'm "pushing him to have sex".

And then he gets quickies just so he can get off whenever he feels like it? I don't think so...

He is uncomfortable with me masturbating on my own.

That is definitely a bad sign, he is probably super insecure and controlling and jealous too?

He'd prefer if I didn't because he says it makes him feel like he's not good enough for me.

Maybe he isn't. Not based upon what you're saying above. That's his problem to sort out. If you're sexually frustrated, solve it. I generally don't recommend masturbating when in a relationship simply because it can cause apathy and laziness which usually results in more unhappiness. But in this case, he isn't holding up his end of the bargain, so to speak.

I haven't touched myself in a very very long time because we were having sex frequently. But now, we aren't and I just want to get off. I don't because I'd feel guilty while doing it, which would ruin it. I just want advice basically on what I should do. I'm really unhappy with the whole situation and I just want to feel like he's still attracted to me and wants to have sex with me

To be honest this sounds like a pretty toxic situation in general. You sound a little needy and a lot unfulfilled, he sounds selfish, controlling and pretty uninterested. I think you both need to realize that you shouldn't be having these issues in the first place. If you can't solve it through direct communication, then it's time to move on. That's my advice anyhow, been there done that. Good luck