Don't want a relationship

Today I became part of a "friends with benefits" agreement! That makes me extremely happy. I don't want a relationship! I got out of a 2.5 year relationship and went 6 months single before getting with a guy 10 years older who cheated on me. My best friend, not the one in my agreement, is bisexual and I flirt with him a lot. Today he told me he likes me, after continuously telling me he loves me. I told him I would love to be with him, but I don't want to be with someone. He got really upset because I told him I had sex with my friend. He said I should've waited for him, because he's younger and I don't think he should be having sex with people! He spent hours trying to convince me! I care so much for him and the idea that I've hurt him makes me want to cry. But is it so bad to just want to stay away for awhile? Right now I like the thrill of going outside my comfort zone! Since breaking up with my boyfriend of almost 3 years that I thought I was going to spend my life with, I've done a lot of crazy things from drinking to smoking weed to sneaking out! I just want to make ME happy for once! Ido everything for everyone and I don't want to date my best friend just to make him happy. I just... Can't stop feeling like I need to hold his hand and kiss his cheek and tell him he's wonderful!! He's so cute! I don't know what's holding me back but I can't be with him right now. He got upset and told me I was NOT to sleep with my friend anymore. Somehow, no matter how much I want to save his fragile heart, I don't care to stop just for his sake! (Don't tell me I'm a whore! I've slept with two people in my life, and I'm perfectly comfortable with that. Also, I have an IUD so my chances of gettin pregnant are extremely low) I really like the idea of sneaking around with my fwb and keeping secrets!! :) any opinions besides hurtful ones are welcome!