Let me tell you. I know EXACTLY how you feel. It's so cool to know that other people (or should I say other INFJs) struggle with this too and that I'm not a sick freak.
Yep, I have a history of doing this.I try so hard to be me - to put forward what I like to do, to share my small world with them and it always ends up that I share their world and my small world becomes even smaller until there really isn't anything left of it or me and my identity - I then panic and fight against it and do something stupid like leave my partner rather than talking things though - because at that stage they're so used to the happy sunny version of me that they can't handle the insecure and paraniod me and it dissolves.... I hate it and I have lived through the pattern over and over...
The fear of me totally destroying something that hasn't even started yet (because I know I worry/freak out about stuff) has kept me from starting new relationships. I, too, HATE this part of me.
It's been about a year since I've been actively working on it though (not giving in to the fear of me screwing up things/caring too much about what my love interest thinks about what I say/do. Living in a spirit of fear is unhealthy (it's founded on things that are all in my mind) and it's probably not all that attractive to the person I want most to impress. I've really begun to make a lot of progress, especially in the past 3 months. People (parents and friends) have been noticing a big difference in how I approach situations now and have commented on it numerous times.
Check out my thread in the NF personals. Maybe we can end up helping each other out