found out my (M24) girlfriend (F25) has an oddly close guy friend and I don't know how to feel

just wanna say that this is basically my first real relationship, currently slightly over 3 months in. The entire time we have been together has been beautiful and blissful, and we didn't have our first argument until the other day.

Basically, there is this guy friend of my girlfriend, they have known eachother for almost 6 years, basically go out together one on one, go to concerts together, etc. Our relationship is long distance, he is in the same area as her. He's been to her house "but not inside". She told me they have openly talked shit about her ex boyfriends in the past.

Another reason why I say oddly close is because she doesn't have any other guy friends, it's only this guy she has been consistently replying to for 6 years. I feel as if I am being emotionally shared with a guy I have never met.

Another fact I found odd is that I asked them how they met and she said twitter, and thus, I asked for her twitter conversations, which she then said she "cleared her inbox to save space". When she said that, I promptly asked her to show me the top of her other DMs, to see if the other DMs were deleted around the same time frame, and then she changed the story to "she only deleted his" and blamed it on because she has a bad memory.

And after all of this, I feel like I am being insecure. I apologized to her, it felt like it was my fault about being jealous or insecure. I genuinely don't know where to go from here. All of my friends and family and my coworkers say that this situation is really fucking weird, and yet I still feel like I trust her and want to continue. I'm so confused as the moment. Do I meet the guy friend and try to catch an inconsistency? Or is that insecure and should I just man up and ignore it. I don't know.