I've always been afraid to admit that the things I love to do (learn / art = art theory grad degree) also make me lonely or perhaps a better term, stir-crazy. Does anyone else have this problem? A liberal arts grad degree means a lot of not talking to other humans and I don't know how to reconcile my passion with my vice. Any suggestions?

My science PhD also means a lot of isolation. I am by no means a people person, but right now I'd say that intellectual stuff - what you call your passion - isn't enough. Giving up all interaction with the outside world (which is what a PhD feels like sometimes) is a BIG sacrifice. I'm not sure it's worth it. Maybe you should talk to some people already doing similar courses - they might have wonderful social lives and you'll be lucky enough to do what you love and not be lonely...

I'm doing an oil painting course at the moment- so that I have 2 h a week were I actually go and paint (without this I would always do it "tomorrow") and to meet people who are not students. After the painting course we always go into a cafe and have a cup and talk about all kinds of things.

i'm only considering a phd now i'm going to live with my partner. I decided against doing one as a single parent as i'd have gone mad with isolation. However, the seductiveness (and so value) of art, writing etc is partly because it is you, alone, with the painting, book etc, and this makes you feel special, the art can work on you in this private space.
So, enjoy being alone with it. But balance (rather than reconcile) it with human company...try meeting people for lunch on a regular basis, share a house (background companionship) etc