Jackie,
I agree with Cate just let it be, they are both so young and we don't even know how to deal with our son and his new life. Craig is still in high school, i think?
My son was just 21 and had not been dating a girl but they had known each other for years and were just starting to date when my son had his accident. She was going to attend summer school at collage and dropped out of her classes when his accident happened so she could be at the hospital. He had asked for her for from the start and when she showed up the next day he was so happy and relived.
she came almost every day for 3 weeks and then she stopped and sent him an e-mail that she was dating his best friend and could not see him any longer as she was getting panic attacts. My son was put into a tail spin as this all happened the day before he came home from the hospital. We have not seen her since and his so called best friend stopped by about once a month, and that is to pay his rent to us as he rents a place from us?

I have tried to talk to my son and tell him there will be others but the injury that having two people that were important to you walk out when you need them both was just too much for him to have faith in any future for any relationship.
Craig at least i am sure understands but i am also sure he would have liked some kind of closure, some day that may happen if they meet again. I am sure that the young lady has had her heart broken and did not know what to do and this was the only way she knew how to deal with the situation. Even much older and more experianced people do not know how to break off a relationship.
I guess if you really wonder how she is doing and if you think Craig really needs and ending you could contact her parents and talk to them and see what they think of her stopping by just to say good luck in the future.
I don't know Jackie we have so much to think about for our children we can only do our best, and i know you are.
gzarnke