My oldest son broke up with his girlfriend, but my youngest son is very attached to her. What should I do?

My oldest son, seventeen, has been with his girlfriend for three years. She was at our house every day. She picked my sons up, took Jason, who is two, to day care and my oldest son to school, and she stays at our house on Saturdays. Veronica is Jason's favorite person in the world. He, like all children, can be stubborn at times, but when he is she can always get him to do whatever it is he doesn't want to. If he doesn't want to have dinner, she asks him to sit on her lap and tells him how good the food is, and he'll eat of her plate. He is freaking out now that he doesn't get to see her. Ever since my son broke up with her, nearly every thing he has said has had something to do with "Aunt V". We saw her at Walmart today, but I was with both of my sons, so we couldn't go and talk to her. Jason started screaming about how he wanted Aunt V and everyone was staring at us. He is taking it very badly, and I don't know what to do. I never expected this to happen, my son and his ex were quite serious. I still don't know why they broke up, but every time I have seen Veronica since then she has been crying. My son is quiet and easily aggravated and doesn't eat as much as he should. They had plans for college, marriage and children. I am pretty sad about this too, she is the first girlfriend my son has had that I've liked. Off topic, sorry. But, I don't know what to do about Jason. He refuses to sleep eat or bathe, and screams loudly if we try to get him to. He is also quite mean to his brother, because he knows that it's his fault. What can I do about this? It is very stressful and I don't know what to do.