Wow, your post could have been written by MY boyfriend!
I've had that before, dreams about exs while I was with someone else, and at the end of the day they don't have to mean anything.
You know you've moved on, and for the best, so I don't think this is anything to worry about. Heck I've had random dreams about being intimate with some of my male friends before, and I woke up feeling kind of WEIRD, but... it didn't mean anything.
Heck some of us dream about dragons and magical fairies... They're just dreams, unless you make more of them.