One of the worst lies that depression tells us is that we're alone. It starts off slow, you have less energy and are aware that you're miserable. You feel like you're poor company, you don't want to subject your friends to your mood so you stay away, but that's okay you don't really feel like going out anyway. The thought of being around other people is off putting, either exhausting or intimidating or so on.
Then if you do go out every glance, every whisper ever laugh feels like it's directed at your. You're surrounded by people who say and act like they like you and your company but you feel it's an act. Ever little thing makes you suspect that they're judging you, laughing at your, or wishing you were gone. You feel very aware of what makes you different and assume that it repels the people around you.
That confirms the idea that you shouldn't contact your friends and you go out less and less. Eventually they stop contacting you so often, maybe they eventually stop contacting you at all which reinforces the idea that nobody wants you around anyway. The solitude that you maybe enjoyed at the beginning feels empty, you feel lonely and you're now isolated but you can't see a way out. You're loathe to contact the friends who have drifted away as you're now convinced they never truly liked you anyway, and you've been out of the loop so long you've forgotten the process of making new friends; and besides, it's not like you ever get out to meet anyone anyway and if you did meet some one you're now terrified of being rejected.
The sense of isolation and loneliness strengthens your depression which makes it harder for you to start being social again so you spiral further and further down.
Getting out of that loop is not easy. You have to be wiling to make the effort and risk rejection. However, if you can you'll be surprised at the results. It's easy to let friendships slide and sometimes I struggle to make phone calls and keep in contact that way, but with the technology available today it's so easy to stay in contact with email, social networking and so on. However you have to make the effort. It doesn't work if you don't contact people and send emails or tweet or messages.
Most of the time when I made the effort with contacting people it paid off and I have quite a few friends and a good circle of acquaintances now. I also have better relationships with my family and I have a pretty good relationship with my neighbors, at least one of whom I'm good friends with. Another neighbor recently brought over a box of lemon and eucalyptus tea because he could hear me coughing with the flu. This is because a) I have really awesome neighbors. and b) I've worked on being friendly to them.
This hasn't been a hard thing to be friendly, with my friend we've both got little boys around the same age so we go to groups a lot together and meet up to chat and have a cup of coffee. It's pretty awesome actually as the boys adore each other as well. I just make sure I contact her as much as she contacts me. My neighbor who brought the tea is just a nice guy and when he asks for favors if we can we help out. Also I gave the 4 neighbors who live closest to us home made cookies for Christmas which couldn't have hurt.
The point is, they're nice people and I'm nice to them and it pays off.
With my other friends what I discovered is that far from being repelled by my weirdness that what made me different was part of what made me interesting and part of why they wanted to be my friend.
I've also discovered that it is exhausting trying to maintain a relationship with someone who doesn't put the effort back into the relationship. There are some friends who you're just not going to talk to very often and who will never contact you first, the difference is their attitude when you do contact them. I have friends I don't talk to much but when I contact them they have a conversation with me and actually make an effort to reply. Other people haven't made that effort and they end up not being a part of my life because I have a finite amount of energy and if someone won't even hold a conversation with me or reply to me when I contact them...well eventually they won't be contacted at all.
Of course this is all easier said then done, but it's true. You can be isolated or your can be social but it's down to you to make the connections. Not every relationship (platonic or otherwise) will work out but it's worth it to try.
Despite what Depression tells you.