Staying friends after sleeping together?

We were seeing each other for a short period of time, I met him through my best friend as he is her boyfriends, friend. We had sex and he told his friend and my friend that he seen us being together as a couple, we were supposed to be going out the other week and he messaged me 'I've been asked out on a date by a girl from my past, we used to talk and things didn't work out but now she wants to give things another try so I don't think we should meet up' then explained he never planned just to have sex then leave and how he still values me and how he liked me but they have more history. Then he said 'I'd still like if we could be friends because you're a lovely girl' then said we will see each other about. He kept asking me to be friends with him but I questioned him as he's chose this other girl over me so why would he still want to be friends with me if he's painting the picture that him and this girl are gonna be in a good relationship? He kept messaging me at the weekend "we're good friends and I don't doubt I'll see you again soon" why would he wanna stay friends if he's chosen another girl and claims they'll be so happy together?