How do i go back to normal?

Afew months ago the one person i trusted and loved too much broke my heart and my trust and as much as i have gotten over him, i just dont know how to make things go back to normal. It's almost like the best part of me died or i just dont care about anyone. Lately i am either alienating the ones i care for or just putting up major barriers by acting like a bitter ***** to repel people against getting too cosy around me coz i wonder whats the point anyways. How do i get myself out of this selfish bitter state and out of this hole i have dug myself into?