Girlfriend of 17months flirted with another guy..feel betrayed?

I am so sorry for your pain. I know how bad it hurts when the one you love sems to be pulling away from you. My only advice is just sit down with her once and for all. Have a heart to heart and lay everything out. Tell her that you expect honesty and loyalty and if she cant give that to you then there is no point in moving forward. If she has already cheated or acted unfaithful it will have to be your call on whether or not you want to stick around. If she is doing that to you now she will prob do it again. I wouldn't sit around and wait to get hurt again. Take a proactive approach and have "the talk" with her. If she refuses then she doesnt love you anyways.