It could just be your mind thinking "what if".

Personally it's been almost 5 years since my last bf and I still have dreams about him and his family. We would've never worked out even had I not moved, the whole situation was just wrong and weird. But still I dream about him. Don't feel guilty for your dreams, you do not dictate what you dream about. You may have control of what you do in your dreams once you realize you're dreaming but even that is generally limited.

I'm sorry that you and your husband fight a lot, it may have you subconsciously worry about how solid your marriage is, this is something that you could talk to your husband about, it may open the door for communication between you two. Hopefully he sees it logically and not as a threat but if you think he'll be offended maybe this is something to just keep to yourself and remember that dreams are not real and chances are he still fantasizes about models and exes himself. It's kinda part of the whole "what if I had chose door number 3 instead" route the mind takes.