College son has been seeing his GF for 2 years, and she is always with him. So when we visit him at college, she comes along and we buy her lunch or dinner. She has also stayed at our house for weeks at a time as they migrate about during the summer (and during COVID remote school). That’s all fine and we enjoy seeing her. We invited her along on our extended family vacation this summer (well, son asked us to invite her), which was a big deal bc no SO had gone on extended family vacation. We had some trouble navigating whether we should pay for her flight or not, as we were paying for everything else. In the end, we paid for some of it and her family paid for some. Next time we’ll probably just pay for everything to avoid the hassle. Met her mom at a function at school once. I suspect we’ll see more of her family during senior year events.
HS son has been dating a young lady for over a year, and we see her parents a lot. Sometimes, just to keep these two from being alone too much, her mom will invite all of us over. We get along quite well, and I would not be surprised if we socialized even after that HS relationship runs its course. HS GF has not taken trips with us though. I don’t think her parents are ready for that.