I've had depression before I know its horrible, especially when you have no one to turn to. The mistakes I made were that I didn't appreciate the people I had around me that could have been there for me, since then I have grown a lot closer o my sister who is basically my built in friend and an old friend. Sounds like you need that one person to let out all your feelings and vent, for me it was always my mum as I didn't have any close friends either. You could visit a counselor or a therapist because it is sometimes easier to tell a complete stranger your problems and since they are a professional it is in their code of conduct not to judge so wont have to feel embarrassed or ashamed.
If this isn't an option for you then try to do something new that will motivate you to do better, join a dance class, join a book club to meet new people that can be part of your life or you could even get a new job. Get a dating app and just have a casual account, this will boost your confidence up seeing how many people are interested and make you feel good, it's a good way to get back into the swing of things in a more casual way. If you are really that bothered about your weight then take it slow and reduce the amount of fizzy drinks, sweets and chocolate for a while, then move onto removing fatty foods and take always too. Then start to reduce portion sizes and try to get your 5 a day in as much as possible. Doing this method helped me to lose weight and was easier than a typical diet that can be overwhelming, I lost a stone in weight :D in a year.
Remember though putting on some weight isn't always a bad thing as long as you are in a healthy weight you should worry about it too much, remember every body is beautiful and we come in all shapes and sizes :D