So i have a major problem with my friend. HELP!?

ok so...theres this guy (lets call him bob) and my friend (lets call her lisa) so...a year ago.. bob liked lisa..then he met me and he liked me more than lisa. and lisa said she was fine with it. well...me and bob never went out because i realized what a cruel and mean person he was! so..a couple months ago bob was being such a d*i*c*k to lisa and she was sooooo mad at him and she was telling me all this stuff and how she hates him. so..a couple weeks ago..he IMs her and they start talking and she starts to like him again. and i feel betrayed cause its like... i feel like she was lying to me when she hated him and she really liked him and thars why she hated him. like.. i feel like shes a faker and pretends a lot (which shes known for doing). and then one day me and lisa were texting back and forth and she just stopped..and i havent talked to her since.. so what do i do? should i stop being her friend? she brings up SO much drama should i just let her go...or give her a 5th try?