I was starting to encounter similar problems a year or three ago, and I'm also pretty introverted. More than that, I got sick of the wasted hour spent getting to the gym, back again, and getting changed before and after.
So I hired myself a stationary exercise bike -- I go pretty hard (HR 160) for 40 minutes, 3 times a week, generally in the mornings (apparently makes it easier to get into fat-burning time). I was doing 5 times a week when I was wanting to actively lose weight. I'm guessing that 3 times a week will do for maintenance.
Beyond helping my weight and self-esteem and suchlike things, it means I actually feel healthier, get sick less, recover from nights of drinking better, and sleep better. Highly recommended.
I hire the bike I've got, as I tend to sweat a lot, and salt's pretty corrosive in the long term. After I wear this bike out, I'll just get the rental people to replace it. You could just buy one, but which ever way you go, make sure you physically try it out first -- don't just buy online.
Life is a healthy respect for mother nature laced with greed.