My husband still has sex dreams about his ex

Me and my husband were having a conversation that led to us talking about sex dreams. It came up that every once in a while he still has sex dreams about all of his exes but mostly the one he dated right before me, and also cheated on me with at the very beginning of our relationship. I kinda shrugged it off like it was no big deal, but my feelings are pretty hurt. I feel like he’s still comparing me to her sexually and physically and stuff.. am I wrong for being upset? Is this a common thing? Or is this just a small part of a bigger problem that I should be concerned about.