How do I stop my friendship with my ex from failing?

I broke up with my boyfriend just over a month ago, and although we were only together 5 weeks we spent 5months before that building up a very strong friendship and talked in detail about getting closer. For a long time he said he didn't want a relationship and I was fine with that because I was happy having a strong bond between us, then we did get together because we both said we wanted more. When we broke up he had been going through a bad patch, and said that us being official was putting pressure on him. Although I was upset I still wanted to stay close as friends because from day one that was always the most important thing to me, but we can hardly talk now. Most subjects end in arguments or silence, including when I've turned to him for help. Before we broke up he was always there for me and suported me with big issues aswell as small ones, but now he either doesn't take me seriously or tells me im over reacting to everything. He doesn't tell me much now either. It just feels like one of the strongest friendships I’ve ever had is failing, even though only a few weeks ago he told me he'd always be there for me no matter what. Because our friendship isn't the same its making it more difficult for me to get over him, which is difficult enough because its the strongest relationship I’ve ever had. What can I do?