Why does my ex keep asking me these questions?

So me and my ex boyfriend still contact each other and hang out together every week ever since our break up 4 months ago
We went for dinner yesterday night and this was our conversation:
Me - have u played golf before?
Him - nah why?
Me - coz i played golf last night , it was so much fun
Him - really? At night? With who?
Me - with friends
Him - do I know these friends?
Me - nah different friends, you dont know them
And then changed topic.. :
Me - I went clubbing on Saturday night
Him - oh really? With who?
Me - umm friends?
Him - do I know them?
Me - yeah you met them at the new years party
Him - oh okay , did u pick up guys?
Me - nah but my friends did
Him - hmmm well you could lie to me , i wouldn't know what u did that night
What the heck?
Why does he keep asking me "with who?" And "do i know these friends?"
Im confused
Why does my ex keep asking me these questions?
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