Why is it so hard to keep friends in your 20s

Okay so this is a bit of a random one but it really bothers me.

I was in a very emotionally abusive, manipulative and controlling relationship from 18 years old until I was 23. So controlling that I wasn’t allowed to see all my old friends from school, so we eventually lost touch, and couldn’t really make any new friends at university. The only real friends I have were ones I met while I was working at my part time job while I was at university, and there used to be 8 of us altogether (mixture of guys and girls)

My issue is that slowly but surely, we’re all drifting apart. One friend moved back home for a job and none of us have seen him since. Another guy and girl in the group went out for a few years, and once they broke up he completely backed off from all of us. Another one still works in the bar scene and never makes any effort with any of us. Another works abroad for half of the year, so when we do see her it’s like once or twice in October. Another moved back to her hometown to live with her parents so she could save up for a house.

I was closest friends with one of the girls; we’d see each other once a week for dinner. We lived in the same town, had similar jobs etc and it was all just really good. Then at the beginning of this year she broke up with her long term boyfriend, and now all of the sudden it seems she doesn’t want to hang out with me anymore. Like, I get it, I’m married and have just bought a house so I don’t want to go out partying all night anymore, but I really thought our friendship was more than just convenience.

Does anyone else find it really hard to maintain friendships in your mid-late 20s? I’m just really scared I’m going to end up with no friends, and I don’t understand why. I’m the most chilled in our group normally, I’ve spent many a night bringing ice cream and tissues round to help broken hearts, I’ve opened up my home to them when they’ve had no where to go, I’m not a judgemental person, I make them laugh when we’re together. Why is this so hard?