What if I don't want to reunite?

When I was in my mid-twenties, I became very interested in finding my birth parents, joined reunion registries and even put ads in the newspaper, hoping for some sort of response. Years went by, and I never found them, but in the mean time, my brother, also adopted, was tracked down by his birth mother. She and the rest of my brother's birth family turned out to be very self-centered, demanding and imposing, and my brother didn't seem to gain much by knowing them. After I met my brother's birth family at his wedding, which they ruined by causing a scene, I had second thoughts about finding my own birth family. Years went by, and now, in my mid-forties, my birth mother has found me. It's a strange and confusing experience. For years now, I have been quite comfortable not knowing. When I was younger, I had the notion that knowing my origins would somehow resolve the existential crisis that I was experiencing back then, something not uncommon for young adults to experience. But after maturing quite a bit, the question of my birth parents' identities was not terribly compelling to me. I have spoken with my birth mother, and she has answered many of the questions I had about the particulars of my birth and about my ancestry. This information is interesting, but it doesn't change anything in my life. She doesn't really want to know much about me. She seems to want me to absolve her of some residual guilt she has about giving up a baby. I told her that I hold no resentment toward her and that any issues I had in my childhood had nothing to do with the fact that I was adopted. I don't feel any bond at all with her, and after speaking with a half-sibling that she did not put up for adoption, I realize that I am very lucky that she relinquished me and did not subject me to the sort of chaos and pain that her other child experienced. She says that when she was pregnant with me, she just wanted to have me, give me away, and go get high. She said that for years, when other family members would bring up the subject of the baby she gave up, she would ignore them and try not to think about it. From what I gather, she only tried to find me after my birth father showed up on her doorstep after fortysomething years and pleaded with her for information about me. (She says she can't get in touch with him now, which may or may not be true.) I feel like I owe her nothing, except perhaps gratitude for giving me a shot at a better life. Now that she has found me, she is dropping suggestions that I should call and email her more often, and that I should make time to drive 800 miles to visit her. I realize that other adoptees might jump at the chance to meet their birth mother, but at this point in my life I just don't feel the urgency to do so. My "real" mother is the mother who raised me, whether I like it or not, and I can't change that. I don't know what she expects to gain from this. I can't be her daughter. It doesn't appear that we have much in common, and I suspect that the best that we could achieve is to be friendly acquaintances. By nature (or possibly nurture) I am subject to being manipulated through guilt, and as I write this, I realize that the nagging, uneasy feeling within me _is_ rooted in guilt--guilt that I am causing dissapointment, but I'm really not sure that I want a relationship with her. I would appreciate any comments or suggestions that might help me gain perspective on my situation. Thank you, A.