(((((((VBC))))))))

That's an awful choice to have to make. Lack of sunlight IS extremely unhealthy for body and emotions. But so is lack of friends. I'm not going to offer any trite, happy-face suggestions for "meeting people," for all the reasons you already know - you've probably already done several of them; your therapist has probably already made the suggestions; "meeting people" is not the same as building a deep support network, which takes years; and most importantly, making yourself vulnerable to people in the way that's needed to build a support network is about the last thing a depressed person is capable of doing.

Is going back to Seattle at least temporarily - and buying a light box and some full spectrum bulbs to get you through the day the day - an option? That would both get you away from the BF and into the arms of your friends at the same time. You could take some time to recharge and investigate new places to live, with your new understanding that you need to better investigate the social scene and the character of the people in any place you're thinking about moving.