I want sex. My partner doesn't

So, I have been with my steady boyfriend for 3.5 years now.

For the first year, everything was PERFECT. And it still is... was? Except for a little detail:

We progressively had sex less frequently. For the last year it has been an actual issue for me. We have spent three months without action. As of today, last time was a failed attempt back on early February.

When we met, I came from having A LOT OF FUN on Tinder, right before we went steady. I actually met him on Tinder. So I had to split from another two steady lovers in order to be with him only.

On the other hand (lol, the irony), he came from not having sex at all, being a full time wanker (as in masturbator, not asshole).

Again, first year was great. We got along really well, we share a lot of things and likes, and we had OK sex (considering he was not experiebced whatsoever). Then I started getting excuses after excuses. My dick is irritated. I'm sleepy, my belly hurts... At some point I got so tired of them I even stopped asking. That's when we started having months at a time without sex.

And we've had the same conversation over and over again: what do you need to do, what do I need to do? What of what we are currently doing is wrong?

Even my friends think he's gay. I've thought so too, and mentioned it to him.

He denies it. Also, he's not asexual, because he does jerk off looking at pictures of other women, which makes me feel I'M the issue (I know I'm not, but that doesn't feel less crappy). I'm not a conventional beauty, and yes I was on my prime when we met (fit, athletic, great stamina). But he's not hot either, and even if we're not each other's type, I learned to look over his flaws and find beauty and sex appeal. I genuinely feel attracted to him at this point.

Then, the last conversation we had, he said this "I don't see you like that", meaning he doesn't want to have sex with me, or that's what I understood. He does love me, and we have an amazing relationship, but without the sex, I do feel incomplete, like just a glorified friend. And it IS NOT about the actual physical pleasure: for me is more about a deepest connection, having a different kind of intimacy with him that we don't share with anyone else.

I'm at a dead end now. Because I don't want to force him to have sex with me, but I'm also starting to lose my own sex drive, I don't find masturbation pleasant anymore, and I'm starting to consider having a side sex partner, although I'd HATE if he does that to me (so logically I wouldn't do it to him).

Do you think this is something a sex therapist or couples therapy could help us overcome? Am I overreacting? Is THIS even normal? I never had a relationship longer than a year, so this one has been the longest and most committed one. I'd love to stay with him for the long run, but this is killing us right now.