the girlfriend of a close friend asked me out I really like her but I also don’t want to lose a good friend what should I do?

so I’ve been friends with this girl for three years now I always had feelings for her she has been dating a good friend of mine for about four months now they argue pretty often so it seemed obvious that they weren’t gonna last long she recently messaged me and asked me if I wanted to be with her I do but I also don’t want to risk losing a close friend over a girl