Exercise a lot. Eat healthy foods. Give yourself time.
Also, I think sometimes it’s helpful to think of relationship loss through ending a relationship or death, as a really bad cold. Suppose you woke up one morning with a sore throat and a headache. You probably wouldn’t beat yourself up or get emotionally torn up by it. You’d wait, and wait until your nose stopped running and your head stopped hurting. Meanwhile maybe you’d watch television, read a book, chill out. Wait. Relationship losses hurt worse, and I’m not trying to suggest they’re as significant as a cold, but after a few days of grieving, I’ve found this helpful—to acknowledge that my body and mind need some time to repair themselves and to recover from the injury. It becomes less about you and the other person, and more about you and the healing.