Does this make me a terrible person?

I've been dating this guy for almost two years and he's such a sweet guy who loves me with all his heart We broke up for awhile, and I found myself interested in my best friend and I felt like I never had before...like electricity was flowing through my body whenever he was around, or even if his name came up. We became even closer because we had both ended long term relationships, and one night, I don't know what came over me but I kissed him. Ballsy right haha..the crazy thing is that it felt so perfect..and it was all perfect for awhile, I'd never been so happy in my life...but we kind of rushed, then things weren't so great anymore..I was just so afraid of being alone, and I realized that maybe I should give my ex boyfriend another shot to avoid getting hurt. However, this other guy is still in my mind all the time...whenever I see him, my heart finds a way to keep rebreaking, and I'm still head over heels. I feel terrible because first of all, when I got back with my boyfriend, the other guy began "talking" to his ex girlfriend again (even though she cheated on him repeatedly) and now our friendship has a huge strain...I feel so horribly guilty and I'd never cheat on my boyfriend, but I can't help to want this other guy more than anything...I'm torn in two because my boyfriend doesn't deserve this, and it just doesn't make sense to let go of something that you've had for so long.. but on the other hand..it doesn't really make sense to hold on to something that's not actually there anymore.. and if I do break up with my boyfriend for him, I don't know how I would get him back... Please help!