Why is my ex doing this ?

so To make a long story short I was with my ex for 6 years but known him for 10 years . we lived to together till i decided to move out of state and he didn’t want to move so he stayed be hide and we tried the long distance relationship but it didn’t work out so he eventually he got a new gf that he posted on social media and everything i was crushed and he been with her for years and in those years i have not heard from him in 4 years since then . so 4 years later i get a text from his number and he is acting like he is another person but i know it’s him so I’m going along with it like he is a stranger why is he acting like he another person instead of telling me who he is why the games ?