What should I do when my gurl is cheating but says she loves me and want to be with me

my gurl says she loves me and want to be with me and we stay together but she doesnt want me to leave. I know she loves this person cause she spends more time with him than me and plus she hides her phone turns it off when she goes to bed. she takes him out and how I know is because I always find reciepts and plus she never answers when I call nor do she text me when I text her what should I do even though I have a lot of evidence thats shes cheating but I love her cause shes real kool and nice and fun also she says I nag too much dats y she talks to this guy she said stop nagging all the time