Why does my ex keep contacting me?

Hey guys, my ex and I broke up after two years of a lovely relationship about three months ago, because he has depression issues and he felt like he was beginning to treat me badly. We ended in a sort of "up and down" fashion, for the first three weeks we were still pretty inseparable; he would message me or contact me a fair bit, but then we had a big fight at an event we went to together and didn't talk for two weeks after that. He told two of my best friends that he still loved me and wanted to be with me, but that he "didn't like the person he was becoming", and that it was nothing to do with me.

Two weeks later we bumped into each other and talked for a bit, I gave him a letter basically telling him that I have accepted the breakup, I still care about him and that I want us to be in each others lives in time but that he did hurt me with some of the ways he was acting post breakup. We met up two weeks after that for coffee (officially to swap things but he ended up not bringing them), and just talked things through. Now we're officially on good terms, but I said I needed some time before we could be close friends in that way. Since then my friends have told me they have seen him around uni, and he looks pretty miserable, as well as turning down girls who have flirted with him. He also asks our mutual friends (two of whom are very very close to me) how I'm going whenever he sees them, and how I'm managing with things.

Since then I've tried giving him his space, I don't initiate contact with him other than to just get my things off him and give him back his key. However, he keeps initiating contact with me via the phone, msn and Facebook just to talk about stupid things about two or three times a week. Some of our conversations verge on flirty/reminiscing about our relationship, and I'm trying to be nice but not pressuring. Whenever I see him, he looks happy but according to others he isn't otherwise.

I have also asked him about four times now if we can swap stuff (so I can get closure on this whole thing), and he says he'll "try to remember" to get it back to me the next day, but never follows up on it. Then, he'll talk to me afterwards as if l never asked, and repeat cycle.

I'm so confused, why is he contacting me? I still love him very much, but at the same time I definitely don't want to get my hopes up about anything else happening. I want to move on, but it's as if he's not letting me, by both contacting me in this semi-flirty/pointless manner and not returning my things. What is he trying to do, is he just trying to buy time for him to decide what he wants (whether he wants us to get back together), is he just forgetful and being friendly (not too sure about this one either as I've asked so many times!), or is he just keeping me on hold because he doesn't want anyone else to have me?

I'm trying to move on, have been on casual dates and just having fun with life, but I know I haven't completely moved on from him.