Uhmm guy friends confusing me!?

Wow ok this is going to be really long. So, theres these three guys. The first onee lets call him Thomas. He's not really boyfriend material but is extreemely good looking and fun to hangout with. The second one lets call him Nate. We'v been friends forever and I have always liked him but im kinda starting to like him. He flirts with me alot in our cles and I dunno. The third one we'll call him Zack. We went out for about a month and a half but i decided to brakeup with him because he was really clingy and needy and wanted a serius relationship when i did'nt.But I still really like him and he's always saying he screwd up and wants me back but I keep saying no. But now tomorrows the last day of school and im pretty sure I have my heart set on one. Nate. But im ot sure if im making the right decesion. Help.?