Is it normal to be in a relationship but still think about your ex?

Heyhey is it normal people,

So my boyfriend graduated and I'm still in college. When he was here I never thought of my ex-boyfriend but now that he's gone, my ex has been on my mind often. My boyfriend's incredible. He's basically my first serious relationship (my relationship with the ex was technically my first and ridiculously short and we only got together because I was a freshman in college and wanted to experience having a boyfriend). Now even though my boyfriend's great, the ex keeps popping into my head. At the beginning of the year he told me he still has feelings for me. Thing is I was tempted... When I say tempted I'm not sure if I mean cheat or just flirt, but I was tempted... I'll leave it at that. Point is, I still entertain his texts (he always texts me when he has been drinking, sometimes just talking about something random, other times saying how he feels) and I never tell him to stop. If he's talking about his feelings, I ask questions. We don't hang out because I think that'll be a terrible idea, but part of me wants to. What I do know is that I'm in love with my boyfriend... Is that normal? I'm confused...