30 Something and Single:
When you make friends, you're not just making a friend. In your 30's, if you make a friend who has a partner, you just made friends with a couple. So don't complain a year into a friendship that you didn't sign up to be friends with this person's partner. It was pretty much automatic.

And if you're in a relationship and make friends with someone in a relationship, you've just entered a "couples relationship". You can make sure that your respective partners get along with each other, but it's not necessary, they have to. And they'll suck it up if they don't get along. Trust me.

30's are much better than 20's in terms of personal development and confidence, but in terms of social relationships, if you're not a couple, it's gross.