What to do?, In the middle of two best friends.?

So back around Christmas time I met a guy that lives far away that was visiting my town. We hit it off really well and had fun drinking and partying all night with my best friend and his best friend. We ended up making out and nothing was akward the next day. He texted me saying how much fun he had and that when he comes to visit again he will let me know. I knew that this guy wasn't someone I was going to put in the serious category for dating and not to invest my feelings even though I could see myself starting to fall for him. A couple weekends later my best friend and his that lives in my town all went out for drinks. We were chatting about how fun the night we all went out was and we were starting to get tipsy. His best friend was flirting a lot and it was charming to me. I hadn't heard from the other guy since we made out and I was over it thinking he was just another guy who goes out and hooks up with girls. His friend which we were currently out with was very sweet and admitted to liking me too! I thought at this point he would be the more sensible person to pursue rather than his friend who was the bad boy that always made me an emotional mess! So we started dating! his friend of course wasnt thrilled about it but understood since he lived far and we only hit it off once. So now we get to current day....I have been dating the bad boys best friend for 4 months now..recently the bad boy was in town and asked me if i wanted to get drinks after work. I was so tempted I had to ! I was determined to keep it very friend zone though. We get drinks and I can tell hes totally into me ..we kiss which made me so guilty but i figured it was harmless and over. He never told his friend that I'm dating...I thought this little rendezvous was over until this weekend when he contacted me again to hang out and invited me over after the bar.. I refused and he asked me to come over three more time clearly a booty call. What should I do the bad boy is so sexy but the good guy is sweet and respectful I feel so guilty because they are best friends! Why would they do this to each other?!