how to heal a heart??

Time will heal you. In the meantime focus on activities that can take your mind off him. Go out with friends, watch movies (avoid romantic ones), go to the gym, start a new hobby... etc. If the person you're in love with suddenly left you for no reason at all, then that person doesn't deserve you. You ought to be happy. Cheers!

A piece of an advice, you should better confront him and have a talk with him on some matters that really bothers you and reasons why he left you. If ever he won't talk to you just let him know that you are not forcing him to come back to you, you just want to know the truth that's all. Let him know that you can survive even without him. But I understand how you feel that you can't let go because you truly love him but if ever he tells you the truth be brave enough to accept the fact and to let go. I know its kinda hard to do it and it is not that easy to move on but come to think of it he is not the only guy you would meet maybe there's more deserving for you. Believe me I've been through that. Just learn to accept the truth and let go of the past then everything will come back into place.

Pray... and God will give you the answers. Bear in mind that even if the whole world leaves you, God will always be around. I know you are hurting so much at this moment, and it won't be easy for you to accept anything at this time. Pick yourself up little by little, and in time, your heart will heal. There is a reason for this to happen. Maybe God has something and someone better for you. Let Him be your bestfriend, your confidante, your shock absorber.. He will heal the pain in your heart and make you a better and stronger person.. God bless you.