I totally relate to this. I have a friend at work at the moment who seems so cool and understanding that it actually makes me anxious to be around her sometimes because I'm terrified she'll get bored of me, stop talking to me and not want to know me anymore. I even had a dream about it the other day - I was talking to her and then she ignored me and lifted up her chair and moved away.

The one thing I have learned from the past (although I'm not the best person to give advice) is that sometimes if you fear something you can inadvertently make it happen. I think I've done that before by getting angry at imagined rejection - which has then turned into real rejection.

Try to enjoy the moments you have with her and enjoy the friendship now. It sounds like a good one so believe her when she tells you she isn't going anywhere