Is he being heartless?

So I know this guy (we went to primary school together) and now I have him on a MSN type chat thing. And we tell each other everything and we have really cool conversations. We recently admitted to each other we liked each other. And now all of a sudden his ex has reappeared and wants to get back together with him. Now all of a sudden he's treating me like his 'little sister' and he said we'd only ever be friends and they're probably gonna get back together. I feel like he's being an *** because I still really like him and he was just lying to me the whole time coz he's so willing to run back to his ex despite his 'feelings' for me. Is he being heartless or am I just overreacting?