1. is he alive
2. people go through shit that they don't/won't share. I have made some changes in my life that not everyone understands; it may feel personal to you but it may be that something completely different is going on that doesn't actually reflect on you at all. You have done your part to maintain a relationship, but if he won't respond, take a few months off and see how you feel. I had some shit dealing with my ex-wife that required me to re-evaluate some relationships and it sucks, but it was ultimately healthier for my personal growth.
3. there are people in your life that are there for a season and that's okay too. not every friendship can or will be lifelong.