I was almost in the same position, only my boyfriend and I had only been dating for about 2 years. We had already gotten engaged and then split; then got back together (so we were on a roller coaster anyway), then we got the news that I was pregnant and he acted much like your boyfriend. After I went into pre-term labor at 28 weeks, he seemed to do a 180. He later told me that it scared the s**t out of him and made him realize how important it was, and that it was coming whether he liked it or not. After that, he went to all of the dr. appointments with me, took care of me; just became VERY active in the pregnancy. Have you tried asking how this pregnancy makes him feel. Too, think~ he probably has a lot of things running through his head. I mean it's a BIG deal having a baby and can be a lot to soak in if it wasn't planned. Since you just found out a week ago, I wouldn't fret to much. Like I said earlier, try to ask him how he feels, what his concerns are, and make sure to relate to him (like if says how scared he is, don't say how excited you are, etc). I would give him some space right now concerning the pregnancy. Maybe you two should do something fun that you both like and can forget about it (pregnancy), it may even open-up the dreaded conversation without any tension being present. Hope that helps ya, but main thing to realize is that you just found out. If you two have been together this long, you obivously have a bond. I think he will come around.
K.