Advice when son cant let go of girlfriend

I would appreciate someone elses opinion on what I should do when my son just cant let go of his girlfriend. My son who is 21 has been dating a girl who is 17 for the last 2 1/2yr. During their whole relationship she was always talking about when she graduates the first the she wanted to do was move in with him. Well she graduated in June and their relationship to a dive almost immediately. Within 3 days after she got her first job, she told him that she hadnt felt anything for him in months. He called me up bawling like a baby and said that he begged and begged her to sit with him and talk about their relationship, she called one of her girlfriends to pick her up and left him there in the driveway, begging and pleading. This was back in June. That night he was so upset, crying saying his chest was hurting, so I drove up to his house and picked him up and brought him home. I didnt want him to stay by himself cause he had threatened to kill himself, at least he told her that. I think he probably said that to see if he could get any sympathy from her. I had really thought that he was starting to get over the relationship alittle until the other day. I got on his computer and he had saved some of the Im's from talking to her on the computer. More or less she said she wanted to party, etc. And he was still literally begging, saying he would party too, more or less do anything she wanted he she would come back to her, he even went as far as saying that he would disown his parents if she would go back to him. Well, this shocked the heck out of me, like someone stuck a knife in my heart. And I have to say in all the Im's he had saved in not one did she give any hint that she care for him at all. It was probably wrong for me to snoop on his computer but I was worried about him and I would have never known that he was communicating with her otherwise. So I unhooked the cable internet from his room and told him that I hated doing it but he wasnt getting back online in this house. So he took his clothes and moved back to the house where he was staying before. Now Im worried to death about him, but Im disappointed in him to. I cant believe he would still want and beg someone who doesnt want him at all. Im worried too that he may be suicidual. Suicide runs heavy on my husbands side of the family. I want to do everything I can for him. But I was thinking it might be good if he would be by himself to reflect on things. He is 21 years old and an adult but at the same time he will always be my baby and Im scared for him. Any advice?