Partner masturbating in private and not wanting intimacy?

I noticed it when we were away a month ago. He was in the bathroom and I heard it but put it down to a one off. But it’s becoming more often. It’s happened the past 2 days when he thinks I’m asleep. He’ll ‘sneak’ off into the bathroom but again, I can hear it.
He seems to be making excuses to not be intimate. I asked him this morning if he still finds me attractive because I don’t feel like he does, he sighed and said I wouldn’t be here otherwise.

I feel I may be overreacting, I have no issue with him masturbating, but I do if it gets in the way of our intimacy.

Any advice?