How to get my Ex-Girlfriend back?

Well, me and my ex broke up about 1 month and a half ago. i flirted with her bestfriend and she flirted back and then she found put. anyway i really love her and idk why i did that :/. we have been kinda flirting and she touches my hands and fingers occasionally and sometimes shell just touch my lips :). i wanna ask her back out but i wanna say something that will give her some closure, and make her beleive i will be faithfull with her next time. i really do care about her so much. and sometimes our faces well get really close (about 1 or 2 in. apart) and well stay there for like 3 sec. but she never looks at my lips, which is a sign of body language which means she wants to kiss me. i feel like i cant live without her in my life.anyway please help me! gimme ideas or what to do or say or something just please help me. i want her to trust me again.