I'm not sure how old you are or if this is high school but it sounds like it. My daughters in grade 9 and its so annoying the amount of flirting that goes on. Lets pretend this isn't school and a couple is having problems etc - its downright painful seeing your partner flirting with someone else...especially if they haven't officially broken up yet. Something else to consider - people shouldn't dart right into another relationship, even if they were officially broken up -that person needs to get over the other partner fully...otherwise be prepared for baggage. Flirting should only be for totally single people. If he has problems with his GF then he needs to air it out with her...not justify his flirting ways by talking about her cheating.