IN DENIAL

This week my son (who lives in Texas) called me to tell me that he and his girlfriend of 5 years got engaged. He gave her the ring while they vacationed in Mexico.
I am very, very happy about their engagement. I never met Donna, but I like her very much. I have spoken with her and written to her often. She is a wonderful friend to my son and supports him in all his endeavors. She is a good mother (has 2 kids from a former marriage), and she is close to her family., and a religious person. Anyway, they are thinking of getting married in Mexico or one of the islands. My son claims he checked airfare out for me and it was inexpensive. 
Why is he in complete DENIAL about my condition?? True, I have not seen him in 2 years (I live in upstate NY), but I do speak with him and e-mail him and he knows I was even hospitalized last year for 11 days.  I finally e-mailed him today and tried to explain that it would be impossible for me to fly anywhere since I cannot sit for more than 10 minutes at a time or walk more than a 1/2 block at a time! It is very painful for me to take short car trips.And even if I was unable to attend his wedding, it would not mean that I cared or loved him any less.  God, this hurts me so much. On some level, I think he will attempt to make me feel guilty about this! But I had to write to him and be as honest as I am able to be.