Am I treading on thin ice?

I'm in this secnerio: My friend dates this guy for a year. She breaks up with him a few days before graduation and the start of summer. She starts talking and hanging out with another guy immediately after the breakup-which was messy. Her ex starts texting me about a week ago. He asks me to the movies. I say yes because he is really nice and funny and could use a friend. We have a lot of fun at the movies. We text all the time. I don't know if I like him yet and we haven't done anything besides hold hands. I told my friend we were talking, because I wanted to be up front and honest with her rather then have her find out from someone else and look like I'm sneaking around. Its summer, so I'm not looking for anything serious and neither is he, but I still feel apprehensive because its my friend's ex. She says she is okay with it, and just doesn't want to hear about anything we do-if we ever do anything. So...think i'm treading on thin ice? People are already talking about us, and its only been a few days. And Its weird because its my friend's ex, but not weird enough that I want to ditch him completely, because he is my friend and funny and nice and I'm not sure how I feel about him yet. Think I'm okay? Or think this is a recipe for disaster?