When your friends let you down is it right to be angry with them?

I have four good friends in my residence and we are all there for each other in the good times and the bad... usually. If one of us is doing something wrong, we tell them. Now 2 of them have recently gotten boyfriends, and I had a hand in one of them getting that boyfriend. now the one is constantly staying over there and not talking to us anymore. we have made plans all 5 of us a number of times, three times this week, and each time one of them will say no and it will lead to everything falling apart. Twice I was the one to come up with the idea because I wanted to go with a friend, and then the friend said lets all go together and when the one bails, all the rest bail and I get left alone. Is it right for me to be angry with my friends for doing this? I feel bad about it, but I am just fed up!