Oh man...I can relate to this.
I can only tell you what my experiences have been. I've been through a lot of painful breakups in school, and I think one mistake that I made was that I didn't allow myself to actually grieve. I always "numbed out" with studying so I didn't have to feel as awful. With that said, I think that it's important to have perspective. My loneliness was temporary. One thing that helped for me to have was the self-confidence that I could get through difficulty, and I held myself to stringent standards of self-care and self-respect.
When I feel rejected in relationships, it's sometimes tempting for me to put more worth in grades, mcat scores, etc. to derive self-esteem. I know that might sound weird, but I can't think of a better way to explain it. One lesson that has been helpful for me to learn (and continue to learn, b/c I am NOT perfect with this) is that self-worth is not about my boyfriend, mcat scores, grades, acceptance to med schools, etc. It's about how I feel at the end of the day about my life. It doesn't mean that I'm 100% ok with all of my behavior. Rather, it's about having the humility to accept and improve where you can, but not beating yourself up over your mistakes.
Sometimes, I feel more in control if I can focus on the MCAT. I notice that I do it if things with my family are crappy (my parents are divorcing), I fight with someone close to me (….long stories, all of them), or I just generally feel like a loser who has nothing to do but study. The MCAT distracts me in a way….but the feelings are still there. "What you resist, persists."
Also, another thing that helped me was to only think about how I thought, felt, and experienced the relationship with my ex-bf. At a certain point, I was so upset about why he wasn't satisfied in our relationship that I took it really personally…like I wasn't good enough. Which is false! I came to see that it's ok that he didn't want to be with me. In fact, the whole experience taught me that I'm happy on my own, and I only want to be with a guy who really added something to my life. If they don't want to be with me, I don't want anything to stop them from leaving, because 1) I deserve better than that; 2) Life is short and 3) I'm happy on my own. I enjoyed our relationship, but I also wanted more than he can give. I felt a lot of closure when I really accepted those things as true.
It's not a personal thing, he just wanted something different, and he's allowed to have that opinion. Idk….hopefully this long, convoluted post will be of some help to you. And no worries about "babbling" on your end. Personally, I find it comforting to know someone out there is dealing with the same stuff. I can't turn off my emotions as easily as some other people, and I choose to see that as a strength. But I sometimes can't help feeling more fragile than the average super-human pre-med type.
in real life. 
