Hi, I'd like to help you with your question.
It sounds like your partner is grieving deeply. It would be helpful for him to have a therapist to assist him in working out his grief. But if he will not go, then there is little you can do to force him. But you can learn about the process of grief and help him, if you feel you want to do that.
During your break from each other, it is alright to check up on him. Let him know you are still there for him and that you care. It is nice to go in person to see him if you feel comfortable doing it that way. It will also give you an idea of how he is coping with his grief. But if you do not want to see him, you can contact him by phone. Doing it by email or text is impersonal, so unless you want to convey that type of feeling to him, I would stick with visiting or phoning.
He probably hasn't contacted you because he is depressed. There are stages of mourning and it sounds like he may have become stuck in one of them. The stages are:
denial, anger, bargaining, depression and acceptance. If he is keeping to himself, alienating friends and willingly taking a break from your relationship, then it sounds like depression. The main thing you can do is be there for him. Encourage him to talk to you and once in a while, offer to help him find a therapist or pastor (if he attends church) to talk to. Be in his company and allow him to talk if he needs to. But be careful of burn out for yourself. Take time away and be with other people. You need to recharge so you can be there for him.
Give him time. If he continues like he is now for over a year or so (without asking for help or showing progress), you may need to reevaluate your relationship and see if you feel you can cope with his grief. However, he will most likely work this through and your support will go a long way in helping your relationship grow.
Here are some books that may help:
Experiencing Grief by H. Norman Wright
I Wasn't Ready to Say Goodbye: Surviving, Coping and Healing After the Sudden Death of a Loved One by Brook Noel
On Grief and Grieving: Finding the Meaning of Grief Through the Five Stages of Loss by Elisabeth Kubler-Ross and David Kessler
I hope this helps you,