Struggling with a broken heart

Really having a hard time with my recent breakup and I feel so sad and alone. Sorry this is kind of long. I don't really have anyone to talk to. We were together for almost 2 years and I still don't know what happened exactly. It's so confusing because he's never treated me bad before until now. He started acting a little weird about 2 months ago but we were still ok, texting each other every day throughout the day and we lived together so I saw him every night and we would talk about our days same as always. But then 1 month ago he told me he needed some space because he was unhappy with his life and was going to head out of town for awhile to stay with a friend. I asked him if he was unhappy with me but he said no, just his life. It kind of crushed me because in the past he had always made sure I knew that I WAS his life. A few days later, I found out that he was back in town and didn't tell me and that he was staying with a coworker. I also learned that he wasn't actually with the friend that he said he was going to visit when he left. I still don't know where he went those first few days or who he is actually staying with now. We just moved here 1 1/2 years ago and he still doesn't know anyone here except for my family and his coworkers. I don't want to make assumptions without definite proof but for multiple reasons, I suspect that he may have cheated with this coworker he is supposedly been staying with. There is no other explanation that makes sense when you put together everything unusual that he has been doing lately and some of the things that I have found in our apartment. The first week he was gone, I told him a few times how much it was hurting me that he left and that I missed him but he still didn't try to explain anything and didn't say or do anything to make me feel better. Two weeks went by and I didn't hear anything from him at all (I didn't send him any messages either) and one day he came home while I was at work and took a bunch of his stuff (anything valuable or important of his was gone when I got home). I realized then that he probably didn't plan on ever coming back so I asked him if he was. He could have just said no or ended things but he just said he wasn't sure. I told him again how I was feeling but he still did nothing to fix things and I realized that the sweet guy who was always there to make me feel better when I was feeling down was gone and no longer cared about me. I told him I couldn't be with someone who clearly doesn't care about me or our relationship anymore and asked him when he could come get the rest of his stuff. All he said was "tomorrow". No attempt to try to work things out, no apology, nothing. I just don't get it. He's always been so good to me and hated to ever see me sad or hurt. If something was ever bothering him or if he was unhappy about something in our relationship he always told me and we talked it out. He's completely changed and I have no idea why because he won't tell me.