As hard as it may be, you need to keep going like you are. Acting like you could care less whether she wants to be w/ you or not. Acting like you will be just FINE w/o her. She's seeing that she is maybe having some fun on the side, but still wants you in her life.
I think a HUGE thing you could do right now is to not text/contact her. Just do what you are doing and let her wonder where you are and what you are doing and let her be doing all the contact. Like YoYo said, let her see first-hand what she's going to be losing if she goes through w/ the D. The grass will not be greener. Partying, etc. may be fun for awhile, but it will get old and the single scene will too.
Me: 38 H: 35 S4, S5, S10 Bomb 01/07 Wanted D - nothing would change his mind Numerous A's prior to D bomb; EA prior/during D bomb Piecing 04/07 Deployed for a year 05/07 Still Piecing 2010 M 11 yrs 05/10