Long term relationship

I have been waiting to write on here for a while but never had the balls to do so. I'm 19, female and living with my boyfriend of 3 years. We moved into together after I graduated high school, he is a year older than me. Ever since we moved in, his sexual drive has been low. Super low. I noticed it almost immediately because he used to always be in the mood to have sex, and at first, I didn't say anything because he works late. And of course, I never expect him to always be in the mood. I would always try to pursue him, but any signs of him not in the mood, I wouldn't push any further. I asked him if anything was wrong after a few months had passed because my self esteem was really low and I had felt like it was my fault that he was not interested in me sexually anymore. We talk about sex a lot, because tbh we haven't found a solution to our problem. It makes me really sad and embarrassed to want to have sex with him when he does not want it. He tries to reassure me that he is attracted to me sexually, but is "waiting for it to be natural." He tells me that sex has become a chore which hurts my feelings even more because I don't want him to feel like that. We don't have sex often, we usually only have it once a month, but right now as I am writing this, it has been almost 3 months I think since the last time and our 3 year anniversary has passed. I'm not sure what to do, I love him a lot and I have no doubt with his feelings for me, but this issue really brings me down.