my husband had a sexual dream about his ex

It’s a subconscious dreams. I would probably joke with my boyfriend about it.

I completely understand why you would feel upset and I would too!
But honestly don't read too much into it. Dreams are actually just our subconscious brain trying to process our memories and experiences.

If that's all it was then it isn't his fault and he may be just as distressed by it as you. However, if when awake and conscious he reflected on his dream and enjoyed it, or made him miss his ex etc then obviously that's a different story. I would therefore definitely talk to him about it without any accusations and ask him to be honest about how he feels about the dreams, and seek his reassurance.

So have you not spoken about it at all? Because he’s obviously aware he’s having the dreams when he wakes up. I’d definitely bring it up. It may be nothing, but it could be something. Doesn’t hurt to ask, especially if you’re married. I’d definitely be talking to my husband about it if I heard him screaming out his BMs name.. and hed most likely bring it up and be freaked out if he were having the dreams too bc it would make him feel guilty and gross.