This must be a frustrating predicament for you. Especially when others are essential for our healing. I too have a similar problem with pushing people away. If I have friends for too long, I feel immense pressure to 'perform'. It makes me very self conscious. I usually make excuses not to go places, stop returning phone calls and gradually 'slip' myself away.
However, this has changed for me recently in the form of a friend named Amiee. Now Amiee is hard to lose. Hard to offend and extremely sweet. A few months ago I was having a bout of severe depression. I had asked my husband to remove all sharp objects and to change the combination on our medicine chest. He forgot his razor blades and I picked one apart and tried to slit my wrists with it. It took so long, I changed my mind, broke down and fell asleep. The next day I had plans with Amiee and called to say I wasn't feeling well. She showed up 2 hours later with a big basket of pick me ups. (Kleenex, Tylenol, a DVD for the kids and Chicken Soup.) I felt so guilty. She did this probably 5 times last year. All after suicide attempts to which I claimed 'I wasn't feeling well'. I found out recently that Amiee is extremely stressed (I knew that she was exceptionally organized) and that her worry about details kept her up all night writing lists. That she would have crying spells for hours a night and that she felt frustrated in her parenting. She told me later that the time she spends with me help her through it. Also, when she is doing service or kind things for others, she is forgeting herself.
I'm telling you this because sometimes we forget that others need us. My advice to you is to:
1. Set yourself up - Find friends now that are hard to lose later. Hard to offend and in need of you.
2. Make your weakness a strength - You are NOT the only person who feels like this. If you listen (and I know your a great listener) you'll find others who are like you. You've dealt with this for a long time and have experiences to share... Share them AND the people your sharing with will have a similar mind set and will be less likely to let you slip away.
3. Give Service. Look for opportunities to make someones day. An elderly neighbour, heck, a younger neighbour. You have a soft heart and much to offer. The bonus with exchanges like this is that they don't last long but will mean alot.
4. Practise online. Your already making friends.... practise keeping them.
You asked for advice and this all I have. I hope others after will disagree and add to it