Is it normal to be with someone new and still think about old flames?

So I'm 21 and with someone new, 3 weeks now. He's so sweet and I feel like it has the potential to be the type of relationship I've longed for since my high school sweetheart broke up with me. I dated nothing but jerks for many years and I know I've found a good guy. But I have a few things that worry me... he reminds me alot of my high school sweetheart, but he def has differences. My biggest problem right now is that I'm still extremely attracted to a close friend I had previous "relations" with. We tried to be together but it just didn't work. My physical attraction is still incredibly intense. And then I have another male friend who all-of-a-sudden wants to hook up because I'm no longer single. Long story short I'm still sexually attracted to a few of my guy friends. And I feel awful about it because I really care for my new boyfriend. I think I'm just scared but I can't be sure. I don't hang out with said friends because I don't want to do anything I'd regret and lose my new boyfriend. Is this normal for me to feel this way? What can I do to stop these "wild oats" type feelings.