Sex with ex in dreams even though married

Ka

I keep having sex dreams with my ex. Even though we don’t see each other. I’m married and been with hubby for nearly 7 years. Me and ex have 4 kids together hubby and me have 5 (yes I have 9 kids lol) my question is? Is why? Mean I couldn’t stand the twat when I was with him but did enjoy his dick. But that’s it