please help idk what to do

So im long distance and decided to be nosey on my bfs phone. I know i will be judged but he has free access to my phone always. So i was looking and he has texts from girls saying they love him with all these heart emojis. Its not one girl its multiple. Ik he only meet these girls in august. I just dont why a girl would feel comfortable doing this. I wouldnt even do this to my best friends bf who i am close with. So he technically did nothing wrong but why do these girls feel so comfortable to do this. He tells me he lives me but if i did this to guys or even text a guy he would flip out. Considering going on tinder/sending myself fake texts to make a point. Should i or am i crazy. I trust him but like i dont want to be oblivious to his actions.  Also this girl in high school was trying to invite herself over to his house at college. So i want to text her next time we are together cause she always asks to hangout with him. If i just say hi whats up or what would you do? Thank you for the advice. It means a lot to me.