Relationship problems....advice?

sooo in a nutshell i am having some problems...i have a girlfriend now for two and a half years but past month or so we have really been getting more and more distant and fighting with each other and stuff...the problem is that there is this other girl (one of my best friends) who i've always liked and now i'm 99.223290234 percent sure she likes me too....so the question is: do i wait and try to get past all the fighting and everything and remain best friends with a secret crush, or do i break up with her and possibly take a shot at my friend after so long?