I understand where your coming from... Last year I was diagnosed with panic disorder and depression, I was housebound for 3 months and I lost all of my supposed "friends" ... I needed to get out though, I don't mind being alone but having someone there for you is a great bonus in life... I joined an Adult Learning Course for Art... everyone is a lot older but a lot more understanding, I really love it and it's helping me start to get back to my normal life... could you try something like that? a course you would be interested in? or a support group? Honestly they do sound crap but they do and can help... I'm only 18 and I see a reason to carry on now... x
Being a social person takes practice. I too sometimes describe myself as a loner - but a lot of it is because I get really nervous when I have to go out and do group activities. I realized that for me at least, it's just because I don't know what to expect.
So I force myself to go out. I'm nervous at first, but I end up having fun. Try finding some general interest courses where you can socialize with people for a short set period of time (and having some kind of organized activity) gives you something all to talk about. E.g. I took a cooking course.
You can also find online groups (e.g. www.meetup.com) where people with common interests can meeting in real life.