A number of times we’ve had arguments and he’s got deeply upset - for me it’s a critical part of a healthy relationship and for my own self esteem.
So in that case you should understand that this isn't a healthy relationship.
He can't make himself want sex for your self esteem.
He’s got so uncomfortable there have been tears when we’ve been doing it and we’ve stopped and argued
This is so worrying. He quite clearly doesn't want to. He's not choosing to cry and make you feel bad.
and feel sad and hopeless that I always have to be the one who brings it up as something we need to work on (by doing).
Of course you're the one who brings it up. He quite clearly does not want to do it.
He’s accused me of being coercive, manipulative and abusive, because he’s felt pressured because I’m annoyed and upset when we don’t do it, because it feels like total rejection which I obviously find difficult emotionally to process and handle.
It IS coercive.
In time maybe we’ll have marriage counselling
Counselling won't fix this.
I'd imagine that he's either asexual or gay, or that he has a history of sexual trauma.
Counselling won't change him being asexual or gay, and while it could help him have a sex life in future if this is as a result of sexual trauma, the likelihood of him getting to that place with you would be tiny because he will now have suffered some sexual trauma within your relationship.
It feels incompatible in a very fundamental way, is it time for me to think about finding a healthier relationship?
Yes