why did my ex who's my friend say this to me when were not talking?

"Liking this girls photo because it's playing on your mind LOL Aw I loved meeting her last night, please lol don't become a jealous" then he ignored me I'm confused why he sent it. We have fallen out when he met they girl she knew me and he mentioned last night to her that me and him were together 3 years. We split up 2 years ago but we're friends now. We have fallen out why did he send it I'm really confused. He met her at 9:00pm then sent that message at 5:00pm the next night. But why?