Have you met this guy? Never believe your GF won't cheat on you NEVER BELIEVE THAT...i thought that way, man was i fvcking wrong. I perfect relationship of 2 1/2 years down the drain...with no real explanation, while now she is currently desperately trying to get back with me.
Meet the guy, you are the Bf, or tell her enough is enough, women like a slightly jealous guy...it shows you care about them.
DO NOT LET HER WALK ALL OVER YOU. If she cares about you, she will not let you feel like this. I've seen this happen too many times and 9/10 the guy gets broken up with. If she is walking all over you, i am afraid to say her interst level in you is very low...which will cause a breakup eventually.
If you do think he is up to something - i am 99% sure your GF would know. Women can see right through men (Not DJ's of course
Some women are attention *****s and you have to set them straight.
And if she puts up an bs defense when you ask her, break up with her. Not many women get broken up with, this will put her in shock and could possibly put her back in your arms much more devotedly or lost forever but who really cares, you don't deserve to live like this. You are the man, you make the rules (you allow women to think they can too haha) and you put yourself in a healthy happy relationship of your standards, not hers. There is always a better HB around the corner who will treat you way better.