I CHEATED ON MY BF - IT WAS MY FIRST TIME!!! (10 PTS)!!!!!!!!!!!!?

I've been w/ my bf Mark for 3 yrs but I cheated on him when his friend Joe poured his heart out to me and told me how he's liked me since the day we met. The thing is I never had sex w/ Mark b4 but I did w/ Joe and he was my 1st time. I kept telling Mark I wasn't ready. After receiving helpful advice on this situation, I started to wonder if I love Mark or if I am in love w/ Mark. I love him but Idk if I am in love w/ him. I honestly think I may want Joe. Mark cheated on me after I told him the truth (I caught him & some girl making out/undressing) although he says he stopped it & it didn't go further. I am upset about it but I hide it around Mark b/c I know I started it. Mark & I started to reconnect but I know he's hurt & things probably won't be the same. But Joe showed up on my porch w/ flowers & saying he likes me. It took everything in me to walk away. What is your opinion on this? I'm thinking I should fight for Mark, but Idk...I had my first time w/ Joe & not w/ Mark. That kind of means something. I left out all the details but could you give me your input? Joe even asked me if I was sure b4 we did it & I said yes. What should I do? Should I fight for Mark or be w/ Joe? HELP! Thx