How to fix this between my friends and I?

Well to start this out, i have been friends with this guy, (benjifranklin) since 6th grade. He has liked me multiple times, and I always was rude and every time he asked me out i would say: "I don't want to risk our friendship." Now that its three years later i really like him. I mean A LOT. The problem is, he has a girlfriend who is also one of my friends, (lissa) and they are like madly and passionately in love... and it hurts. When he calls me i give him good advice, (Benjifranklin and I are best friends)and i do try to keep them together, even though it hurts so much. But there's's another part of this problem. another guy in our group of friends (Kustin) likes me. SO its kind of like this. Kustin likes me a lot, I like benjifranklin A WHOLE LOT, and lissa and benjifranklin are madly in love, and want to stay together forever. (this is their 10th time going out). And I want your opinion on this situation please?