my best friend is having issues with her boyfriend again?

ok so my best friend of 5 years is having issues with her bf again..she broke up with him b4 because he was playing 2 many games with her but then after she broke up with him he started reminding her of the things that they had did when they were together like playing their song, things that he had wrote her and bought and all of that good stuff...so after all of that she decided to go back out with him..so now after about 3 months now he started messing with my best friend again and she is just tired of dealing with it..i tired to ask her what was wrong and she said that she didn't feel like talking about and she hasn't txted me in awhile because of this...i'm very worried about her because i love her she is like the lil sister that i've always wanted and i'm like the big overprotective brother that she loves and always wanted...so my question to you guys is when she txted me back about this situation what should i tell her to do because the last time i told her 2 break up with him she did and then they ended up back together because of the reasons why i just told you guys so what are you guys suggestions

oh and by the way i'm 17 and my best friend is 15