Feeling Abandoned by my BBrother

In 1963, my mother gave birth to a baby boy out of wedlock and at birth he was adopted by a wonderful couple who were affiliated with my mother's church. My mother married my father in 1964 and I was born in 1967. Although I was very young and too young really to fully comprehend the situation, my mother periodically showed me photos of a little dark-haired boy who she said was my brother. When I was in my 20's, my brother made the choice to find our mother and meet us, along with his wife. For the first couple of years we had a good relationship, although there was always tension and jealousy on the part of my mother whenever she learned that my brother had contacted me but not her. She tended to get a little dramatic about these interactions and would send cards and notes to him that would make him feel guilty. My mother passed away in 2004, and my brother and his wife traveled more than 600 miles to be present at her funeral. In the late 90's my husband's job sent us to within 70 miles of my brother's home and as a result we ended up seeing him and his wife more often. I was invited (once) to a birthday party his close friends threw for him - so they could meet his bio sister I presume - and a couple of times my brother/his wife had us down for Thanksgiving. We would periodically visit them at their home and vice versa. I was NEVER very comfortable at their home. We had several small children, they had none. We are far simpler in our tastes and activities, they had affluent and sophisticated friends. I always felt that my brother's wife in particular was a little on the "snobbish" side. As time went on, it became apparent that my brother's wife really wanted little to nothing to do with my husband, myself and our children. She stopped coming with my brother when he visited us, the invitations to THEIR home stopped coming. With no explanation. I know this sometimes happens in adoption, and I tried not to take it personally. Then, in 2005 when I gave birth to my son, we received not so much as a card from my brother and his wife. This was hard, since I had traveled to the hospital to see him when he had major surgery, and they had come down to see us when our daughters were born. To this day, my brother's wife has never laid eyes on my little boy. My husband celebrated a 40th birthday in September 2006. I invited my brother and his wife to come down and share the day with us, especially since my nephew from Arizona was in town and my brother had never met this BNephew. The day was nice, but my brother seemed in a bad mood and was clearly resentful towards his wife about something. She had not joined him on this visit. When he left, abruptly and angrily (I have no clue why), it was obvious something had happened between them before he came to our home. I got the sense she didn't want him to come see us. I sent him emailed photos from his visit and told him how much it had meant to have him there with us that day. I never heard from him again - until this past fall. TWO FULL YEARS HAD GONE BY. When he finally did choose to communicate with me he wrote simply "I'm sure I'm the last person you want to talk to, but I just wanted to see how you all were doing." He also sent me an email at Thanksgiving asking to see photos of our new house. To date, there has been no explanation whatsoever for why he essentially wrote us off for two years. I have no idea what to say to him. I want to know why his wife stopped seeing us, what we did to deserve to be ignored for all this time. I know we don't have as much in common as we seemed to when we first met, and I believe that has something to do with it. I know they are close to a very wealthy family (dad, mom, daughter in her 20's) who they travel with and that the daughter was always jealous of my relationship to my brother - who she considered like a brother. This post is already too long, but I would appreciate insight from others in similar relationships with siblings who were adopted away. Should I ask my brother WHY he wrote us off, what we did to offend him and his wife?