What is happening here? How do I proceed?

I am a 33 year old female and recently met a 28 year old man at a work function. A few weeks later, he started pursuing me and we began dating. It was an awesome relationship at first. He told his parents about me, introduced me to his friends, sent flowers and sweet text messages and was a great guy. One month in, his calls started dropping off and I sensed something different in him. When I asked him about it, he brushed it off, saying there was nothing wrong and he was just busy with work, etc. Finally, after some pressing, he told he he wasn't feeling a spark or feeling like he was falling in love with me and in other relationships, he has had those feelings much sooner and wanted to tell me so that I could decide whether we should continue dating and see what happens or just cut it off. I was pretty taken back because all indications pointed to him really being into me. His best friend even told me that "John" was like a kid on Christmas lately because of me- really happy and excited. I told him to take some time to think about what he is saying to me and get back to me when he had some clarity. I think one month is too soon to write someone off completely and if he had those feelings before, then where are those girls now? Didn't work out too well there, did it? After a week of no contact from him, I gave up and told him so. Because we work at the same place, different department, immediately after I said that, he made an excuse about work to contact me and request to see me. I had a death in the family and told him about it and he became very apologetic and sweet, sending several messages to offer support. Normally, a person says "let me know if there is anything I can do" and they leave it at that. This guy sent 5, maybe 6 messages offering support. I perhaps got false hope, but got the impression that he was trying to get back in good with me. I happened to run into him at work the following day and he was very stand-offish and cold to me. I just don't get what is going on with this guy. Super sweet one minute, never giving an idea that something is off and then cold the next. I really care for him and thought we would be a great fit, so I am not sure where all of this "not feeling a spark" came from because I have been dating since a teen, so I know a spark when I see one and he was definitely feeling one. His friend wouldn't have said what he said if the guy wasn't. I know he hasn't met anyone else, so I am just confused as to what is going on. After I saw him at work and he was cold, I asked him to refrain from contacting me because he wasn't the person I thought he was. I decided to shut the door and not allow his back-and-forth attitude to mess with my head, but it hasn't worked out the way I hoped. I still miss him and want so badly for him to "come to his senses". I just don't want to hold out hope, so I figured it was the right thing to do. He has contacted me, asking me why I am so upset with him and I haven't answered. I am just wiped out. I guess my question is more of how I proceed next. Do I answer him if he texts/calls me again? For being so experience on the dating scene, I am really thrown for a loop with this one. Any advice would be appreciated.