My boyfriend of 2 years isn't interested in s*x anymore

First post ever, I'm sorry if it's not done right.

My partner (m22) and myself (f23) have been together coming up to 2 years. We were housemates before we dated (and high school friends before that) so we've always lived together, and still now have our own rooms. We sleep together in "my" room every night and "his" room just holds his clothes.

We have a loving relationship. He works 2-3 days a week, while I stay home and cook/clean/run errands etc. His work is usually 4 or 5 hours at night on a Friday and Saturday, so he's mostly home with me. When he's not working, he's playing video games. I'm not someone who cares, if I'm not relaxing watching Netflix I'm playing with him.

We go out together for food dates fairly regularly, eat most meals together watching TV. There's no problem with our affection, a kiss or a cuddle is readily available between us 24/7. He tells me he loves me and I'm cute regularly. We shower together most days, and always send a "have a good day" message before he starts work.

Basically im saying, there's no issue in our relationship. We are solid. We are very comfortable with one another, have no secrets, always on each other's team.

I feel like a major asshole for my "problem". We have sex, maybe, once every 2 to 3 months. In November 2019 we had sex, then in January he let me give him a bj and around 2 weeks later in January we had sex again (uncomfortable shower sex), and then nothing since.

Now, were both relatively attractive. We aren't lazy people, we're fairly fit and healthy. There's been no major changes (weight gain/loss, job stress, home stress, etc.) Any time recently. When we first started dating we had sex every day, and after a year it was more like one a week, but now it's almost unbearable.

To clarify I would never cheat, but it is affecting my self esteem now.

There's no chance he's cheating. I do almost everything around the house so outside of his work of 10 to 15 hours a week, he just gets to relax. I understand mental illness could be affecting his libido but he still masturbates regularly.

When I ask him about it, he has a different answer every time. He's tired, or he's sore, or he's just not in the mood. I try to be understanding and not selfish, and 100% never ever make him feel bad for not wanting to.

I guess my problem is, my mind automatically (after this long) is convincing myself I am the problem. I dont make him hard in the shower, any time I try to be sexy he just says "you're so cute" and brings it back to a romantic situation instead of a sexual.

-- TL;DR Boyfriend of years not interested in sex, definitely isn't cheating, still seems to be horny, but our relationship is great and I am relatively attractive. --

So the question, what might be some alternative reasons for this happening?

I need to stop feeling like it's all on me and my appearance before my self esteem starts affecting other aspects of our relationship.

P.s. I have brought this up to him, and then he acts OTT sexual, and I have to tell him I dont want pity sex, i want him to WANT me, which then just ends up in an "oh.." and he's back to not being interested. I could stand naked in front of him and get nothing.