One day he acts purely like a friend, the next one tries to seduce me? What's up with that?

this guy and i,have been friends in the past 2 years.when we met,he was coming on to me a lot but i rejected him every time he tried,not because i didn't like him,but because i thought he was a player.in the meantime we developed some sort of brother-sister relationship and we both moved on with our lives and we both now have different partners.but the thing that bothers me the most is the fact that sometimes he acts like he still likes me and then there's other times it seems like he doesn't.one day he's all flirty and trying to seduce me and then the next,he shows me pics and videos of him and his gf hugging and kissing.then again after a few days he tries to flirt,and the next day he wines about his gf to me and begs me to help him make her jealous....one day i'm his bigger sister, and the next he undresses me in his mind. what's up with that? and btw, he have never ever asked about my relationship and my bf, he acts like he doesn't even exist.what does he want from me, i don't get it.what is he doing?