I started going to tech meetups in the nearest large city. The tech scene is utter crap there compared to SF or Boston but I get to interact with a few smart, like-minded people almost each week. My wife says it's been good for me.

Marrying the right person helped. I'm quite in the opposite situation from you: I married for the first time in my mid-40s. I know what it's like to be alone, and to an extent I grew comfortable with it. Now that there's someone in my life, I'm all in disarray. That's not a bad thing, as I've been forced to grow to become worthy of this: two humans, six nonhuman animals, love filling the house.