Would like some advice in terms of partner intimacy

We have a great relationship and have been together for over a year. We have consistently been struggling with this so are looking for advice.

The relationship is me (F) and my partner (M).

I don't identify as asexual but while researching this issue, we came across this forum and it had some relatable posts. Therefore we thought this would be an appropriate place to post.

Basically my boyfriend has a strong sex drive and likes physical intimacy a lot more than I do. I do enjoy having sex once I'm in the middle of the act, but it feels like everything else getting up to there is impossible. I am diagnosed autistic and have been struggling with PDA and OCD in other aspects of my life (eg work) so was wondering if that could be the case here too. Currently we have sex around once a week but often between that, M will try to initiate and I have to reject him. I would like to have sex, I just can't for some reason. Obviously this makes me feel bad as I don't want to reject M, and it affects his self esteem too.

M doesn't want to make me feel bad/uncomfortable in terms of this issue. We would like advice/further signposting if anyone has any ideas on how to reconcile this issue.