<human>: Can you provide a brief rundown of the text in within 3 sentences?

My friend (female, age 19) and her boyfriend of 5 years (age 19) have had this same repetitive fight for about the last 2 months - as far as i know. She has a lab classmate who she has known for about a year, as a mere acquaintance. He is known for being a decent looking guy but she told me she does not have any feelings for him whatsoever. her bf, however, will not understand this. This has been weakening the relationship for a while now and i have tried to give her advice (like what to text him and such) but he will just not comprehend that he just simply needs to trust her for this to be over with. She doesnt show signs of liking him either. they talk maybe once every two weeks if that.  ALSO, her bf is talking to a girl he has a history of liking. my friend stopped talking to this guy for a while for the sake of the relationship, but her bf failed to do so and continues. he does not talk to her regularly, but probably as much as my friend talks to her classmate if not more. every time she tries to talk to her bf, he replies with backhanded remarks only to progress the argument, not helping the relationship whatsoever. any advice would be useful, thanks for taking the time to read through.
<bot>: friend (female) and her bf have an ongoing fight. She has a male acquaintance, who she does not have any feelings for. bf doesnt comprehend (trust issues)