I feel you. I'm really good with first contact (actually it depends on what kind of first contact it is) and I have no trouble dealing with strangers, for example. It's the people I see on a daily basis, semi-acquaintances or people I "know" in some way that make me feel pressured.

Is there any chance you may have opened up (making an advance in your relationship) to this person and then got intrusive thoughts of being judged about it which made you regret opening up in the first place?