How to deal with losing a good friend.

So I became good friends with my exs little brother since December of last year we'd share and talk about our day and what not. We were becoming close. Recently on new years eve, he ran into his ex girlfriend who he dated at 15 and she was 20 yes 20. And now hes chosen her and completely stopped talking to me. He had messaged me that they talk and his current girlfriend hates his ex, and me too I feel upset and hurt. How can I deal with this? I kinda cried about it because I looked forward to talking to him. And the reason I talked to him was because me and his older brother had a kid together so I had a reason to still be around. 😪