Question - hard to stay away

I realize what I have to do regarding this guy. The problem is, he is involved in a group that I will keep on seeing. This is something that I can't give up because it's too important to me.

First question... Should I call him and tell him how I feel, and question him about the STD's, or should I wait and do it in person, since I will be seeing him basically on a weekly basis.

Second question... How exactly should I say it to him? I want to tell him, that I've heard some stuff and it's something that I don't want to get myself into, and also to tell him that I don't want just a rebound sex relationship, and that's all that I see him looking at this as. I also want to keep it kind of cool, because I don't want it to get weird among the group.

Any ideas? I won't be seeing him this coming up weekend. So hopefully that will help cool things down, and I don't plan on calling him, (he just gave me his number last weekend).