My friend is acting really weird with my girlfriend

I've had something similar in my mid 20s. I was on the opposite end, I was the loner and my best friend was the one with a wife.

If you don't what to read the wall of text skip to the last paragraph.

I've never really engaged with his wife to the point of texting and being chatty with her and we never really got along that well, but I did admittedly act weird around her. It also gotten to the point where I was hesitant to enter their house when invited and also almost completely broke contact for several months right after their wedding. By acting weird, I mean I behaved like I always did with my friend - fart and shit jokes, hitting each other for fun, drinking beer, just general dicking around. He clearly had fun, otherwise he wouldn't invite to hang out almost every weekend. In my eyes, she was still fairly new to his life and I've been there for more than a decade (this was way before their marriage). But through the years it became clear that this wasn't one of his fleeting relationships and she was there to stay, so I tried to treat their relationship with more respect, but you can't really change first impressions, can you? In the end it was just small miniscule things that slowly wore me down. Small gestures or phrases that stuck with me and rang in my head for years.

When we were younger and still partying she was often our designated driver. And not the straight edge at the party, but more of a get a call asking to pick us up at 3am kind of designated driver. And since I was the usual suspect in these endeavors, I clearly fell even lower in her books. And I'm a pretty self aware drunk, I still know what's going on around me but I feel like a puppet with loose strings. So one night my friend, another friend and I are out late again and he calls his wife to pick us up. Understandably, she gives him shit for that and they argue over the phone. In the end she agrees. After he hangs up he rolls his eyes, shakes his head, looks at me and says "think twice" in the context of me being hopelessly single.

Those two words stung like a bitch, it's probably the meanest thing my friend has ever said to me without even knowing, I'll probably never forgive him for that. He didn't even know how good he has it, even just having somebody to call. My friend doesn't even know what loneliness feels like, he has a great family on both sides, he always had back to back relationships and generally gets along with everyone. So this personified Golden Retriever is basically telling somebody who's starving to be picky with their meals. At the time I thought 'Fuck him', but that was probably the alcohol getting to my head.

So as we grew older, clubbing slowly turned into grill parties and evenings playing board games. I didn't have my own place so those were mostly spent at their apartment. But every now and then I put in the effort to invite them to my parents house. Till this day she hasn't said 'yes' once. There are always excuses not to come to my place. Mind me, I wasn't a basement dweller, my parents house was in a nice suburban part of town with a cozy little garden. Over the years I probably invited them over 30 times and her suspicious absence always led to me and my friend just watching TV and drinking beer. So one time I asked him straight up why his significant other always declines my invitations. He chuckled and said 'She's afraid of you.' For him it was probably a joke, for me it wasn't. Like I know I'm far from prince charming and have a face for radio, but an actual woman being afraid of me was fucked up. I never made any advances towards her, I have literally zero attraction to her what so ever. I was always as friendly to her as you would be to a colleague, at most I was maybe rude because of my social retardation. So not knowing what I did to scare her I tried to minimize contact with her as much as possible, to the point of not wanting to be in the same room as her, which given that they were living in a studio apartment meant that their whole place was essentially of limits.

But I also started to grow weary of her through the years. She was constantly ridiculing my friend for his hobbies that didn't include her, she complaint that we hang out to much even though we maybe spent one Friday evening per month together, she dragged him in her family affairs, whether he wanted to or not, you know the usual girlfriend shit.

The more time passed, the less time I got to spend with probably the only person I would genuinely enjoy spending time with. I'm very introverted, so finding somebody that doesn't make you feel lonely but also doesn't drain you is very special. I can also admit that I was always living life though my friends. It's not that I wanted my friends relationships to fail in favor of me, it's that their increasing lack of presence in my life shined light on my loneliness and mental issues. Things that I didn't want to deal with. Their wedding was probably one of my lowest points mental wise. I understood that afterwards they will want to spend a lot of time together as newly weds do. So I congratulated them and left them alone. Days turned into weeks and weeks into months. I almost came to accept that this was probably it for this friendship until a third friend brought us all back together. I've acted like everything was fine and we caught up on the last few months. Afterwards the friendship retuned back to normal. We still hang out as much as we can, I've come to accept that his wife don't have to be besties and that for him she will always come first. Like I said, I kind of outgrew the whole situation. It is what it is.

So in retrospect I can say that most of this comes down to my own issues. The fact that my friend found a significant other just slowly drove a wedge between the only one who was tethering me to a social life. I wasn't jealous of him having her, but him having a life I've never had. I've also learned that sometimes it's small throwaway lines or gestures that you don't think about that will hurt people the most. I don't think there's anything you could actively do to help this. I had years to think about it and there's nothing my friend could've said or done to help me either. I'd say it's has something to do with mental maturity and self acceptance, but since you're older than me, it still might be a coin toss.