I feel this to my core. I recently got married. But because I was always the single one of my friends until my late 20s and then again for 5 years in my 30s I get it. I so get all of this. I lost friends to marriage and motherhood.

I think married people also end up socialising with other couples as it all fits so "nicely". The reality is I think folk feel threatened when there are some single people in the mix incase they try to lure away one of the marrieds. Well bollox to that, I don't conform to all that BS. I make sure to contact my single friends, probably more than they contact me. :-)