Why so much mixed signals?

So i got this friend whom i like a lot, but he has a gf now..
He tells me when shes gone he liked me but then as soon as shes around he plays his Playstation.
We chatted 4 times when his gf was on holiday..then since shes been back..he only se ds hey whats up messages...whys he mixing the signals? And if he flirts when with her..woukdnt he do the same if with me?
Granpa always said , The hardest relationships to keep are ones not worth your tears."