Help with my boyfriend and another guy?

So I met a boy last summer, we'll call him Jim. Well, Jim and I went on about two dates before he had to go off to California for college, we talked while he was there, and in about November, I befriended his cousin through Facebook because he liked the same music as me and stuff, (We'll call the cousin Fred). Well, Jim and I talked on Facebook all 5 months, until Jim came home for Xmas vacation, he said that he wasn't ready to make a commitment, and I understood and it was fine. His cousin, Fred, started asking me if I wanted to hang out, and I did, and we've been dating ever since. Jim is completely cool with us dating. It's been about 5 months that we've been dating, and now Jim is back for good. The problem here is that Jim still likes me. It's not that I don't love Fred anymore, but he has been different lately, and the way our relationship has been is leading me to wonder about Jim. Fred and I are still happy, and I feel really guilty about thinking about Jim. Jim and I still talk, because we're still good friends, so he flirts with me a lot. I want to hang out with Jim, but I know it will be a bad idea because I don't want to upset Fred, who is still my boyfriend. How can I stop myself from seeing Jim in a "curious" light, but still remain friends with him, and still remain loyal to Fred? I know it sounds shallow, and it is, so no need to tell me so. I told Jim to stop flirting with me, but I don't think it's going to last for long...I don't want to mess things up between Jim and Fred. They're not only cousins, but also really good friends.