My gf and i have been dating for 4 years and we know each other since childhood, we have had tough times and thats when the guy tried to slip in. He came from a different city just to meet her and when they talked he advised her to leave me instead of trying out, thats when i realised something is off. Anyways we didnt separate and worked things out but he became a regular name from then, he used to send her texts calling her beautiful etc. since we were already in a tough spot i didnt say much but i trusted my gf and soon after 2-3 months she told me he directly flirted with her that too something sexual thats when she realised she should limit things with him. Now after 1-1.5 months , we both were in different cities and our schedules didnt align so i was unable to talk to her and thats when she started talking to him again, not regular chats just few hi ,hello and weather kinda stuff. One day i came to see her and had to text someone from her phone as my phone died and thats when i saw his messages, again he was actively trying to flirt by calling her beautiful etc. i ignored it and later confronted her she defended him by saying he is not flirting and i am not replying in that way even if he is flirting. I was upset and angry but she still defended him by saying he didn’t say anything inappropriate,but tbh it was clear as a day flirting though my gf didn’t reply accordingly. And to top it off that guy is in a relationship for 2-3 years. Is she not as innocent as she seems or is she really dumb that she cant recognise that this guy is flirting with her? AITAH for not understanding their friendship!

Update : She blocked him asap when i told her this isnt right and im not comfortable.