I think it's a case of unhealthy relationship skills. I get close to people because they make me happy, are positive, seem to care about me, are there for me... They are effectively filling my void. But I end up smothering them. And when they are no longer in my life, my whole world crumbles.
Like it happened recently - I'd known this person for about 4 years, but only via internet, e-mail, texting. I finally decided to meet her in person and it was great. We are both horse mad and both bipolar, so there was a lot in common. She helped me through plenty depressive phases, and I like to think vice versa. She believed my relationship with my bf was toxic and when she realised I wasn't prepared to leave him, she called off the friendship. 4 years of it.
Now that hurts. WE were like best friends. I am now too scared to form any friendships again. On the whole I think I'm handling this ok, but it's also left me empty.

On other ocassions, I know I get too close to people too soon. I'm learning to identify these situations though.
And with my T - I put her on a pedestal too, she becomes everything to me. Even thought i could never discuss it with her. I just cling to people all the time...