Why doesn't he talk to me anymore?

so i been talking to this guys for maybe like a month he has a girlfriend but then he tells me they broke up(&i think he lying) and through out the whole month we been talking its like flirting and stuff and all of sudden he just stops texting and skyping so I just wanna know what going on with him. FYI: he's seeing his ex or not ex in a few days and my sis thinks he stopped talking to me so that I don't text him or something when he's with her.

so PLEASE guys and girls help me cause I really started to like him!
Why doesn't he talk to me anymore?
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