Why does my ex keep bringing up the past?

My ex and I were together for 3 years and broke up 2 years ago. Once all the dust had settled we started to talk and became friends again. We have been friends for about a year and just recently I moved to another country. He still talks to me, but lately the conversations have become really strange. First he started asking me about how I used to enjoy sex with him, and what he could have done to make sex better for me... he has a new girlfriend now, so I assumed he was feeling insecure about he sex skills so I reluctantly gave him some pointers. Then yesterday, he started "joking" that I should send him naked pictures. I told him no, he would never see me naked again and then he asked "but what if we get back together?" and I said "I highly doubt that will ever happen". He kept asking and asking why I wouldn't want to be with him again. Eventually I told him that he criticized me too much and made me feel insecure about myself and that I never had self-esteem issues before we were together, and don't anymore now that we are apart. Then he got pissed because I was blaming him for our relationship ending and went offline.

But what is that? Why, after 2 years is he bringing all this stuff up... he always used to joke that I was still in love with him, does he really believe that, and why would he ask about getting back together when I am in a different country... there is literally an ocean between us!