I've been dating casually a month after my breakup with my ex. On the weekend, I met a guy who was also just out of a breakup and we really hit it off; so much so that we ended up having sex. I really enjoyed it, but I can't help feeling somewhat guilty, even though I know I never want to get back with my ex again. We were together for 5 years, and this is obviously the first guy I have slept with since my ex. I don't understand why I feel guilty.