This is one of the biggest challenges of creating a sustainable SM career. Here's one of my strategies for creating a social life:
When I know I have free time (or am feeling that same sense of isolation you are feeling), I think of the people I REALLY want to see. Like really, really want to see - no drama or complicated feelings involved. Then I send out a bcc email to all of them, admitting it's a "mass email" of sorts, and that I'm looking to book my time with the people I care most about. Then I list my availability and any social vibes I have. Literally, I've sent out a day-by-day schedule of my availability (listing my show calls, dinner breaks, curtain down times for each specific day). This is especially helpful for non-theatre friends because they don't get what tech is, or how long a dinner break is, or that we might be free for coffee on a Saturday morning.
Then I say, "you see a time you're free? Reply back and the time is yours."
This strategy works really well because it removes the back-and-forth of schedule juggling between 2 parties (can you do Thursday? Oh, I can't do Thursday, is Friday good for you? etc.) A few times, I've had 2 people "claim" the same time slot, which was fine too - friends from different corners of my world met for the first time, and we had a blast.
Good luck! This is a long-term problem that you are smart to acknowledge. I'll be interested to hear other folks suggestions to this point.