Dad issues. Help!!!!!!!!!!!!?

Me and my dad used to be really close but it's hard for us to talk now. I'm real chatty but right now I just feel depressed. Maybe its the weather? Well anyways since I've been feeling this way I've been paying attention to things more. I notice that my dad doesn't give 2 shits like he used to. I mean hes got a online gambling problem (he doesn't use real money though), and I used to think "Ok... whatever." But now (maybe he always does this) he doesn't even look me in the face when were talking, just glued to a screen. He just goes "Mhm" "Ok" and he always gets happy when he wins something and I get so sad. Even when hes not on the computer I tryed to get up the energy and make him laugh but he was like "What?". How do I tell him my feelings, because I don't think he will listen?