Hello, coriandermay,
As I do many times, I must agree with OronD, (2 thumbs up). This "relationship" you describe sounds like a painful situation, even in the drama filled activity of a student. We've all gone through similar situations growing up and they always end up the same; a painful learning experience. We do learn however, and that is, to honor ourselves and stay away from dishonorable relationships.
Your description of this on and off relationship expresses nothing but pain and distrust. It seems to me that you might be looking for an answer that confirms what you already know. I have empathy for your situation; however, you are allowing this to continue. It is important that you respect yourself, and with that you will know exactly what to do.
With Kind Regards,
Daniel