Sounds like the problem is more a knock to your confidence through the depression etc than the weight gain in itself. The weight gain is probably symptomatic. You won't be able to just lose it if you're not in the right state of mind.
I would suggest you see a doctor, get some counselling. CBT might benefit you as it changes your way of thinking. Seems to me that how you relate to people has changed because of how your personality has changed. I'm guessing before you were depressed you were more outgoing, you were happy with how you looked, more confident, this would have showed to the people around you and drawn people to you.
Excercise will help your mood and manage your weight. Maybe join a gym or find classes to go to. Make yourself go. motivation can be hard. sometimes you need to not allow yourself to have that discussion with yourself
Loughborough at number one