Also there is his dad that poisoned his mind about E.N.D. when they fought.
exactly! like they blamed it all on E.N.D. when he's doing nothing but getting the blame only because zeref created (half-resurrected him since technically he's the brother) him.
Even if that is so. I believed that gray has no right to fight natsu. Think about it, he should have think more before he act n its kind of waste after what they have been through, its like gray is running their whole friendahip, so pissed off at him (╬￣皿￣)凸
He fought with natsu because he thought natsu is losing his mind since invel told him that all demons created by zeref will think of nothing but wanting to kill their creator. So when gray found out that natsu is END plus with natsu saying about killing zeref, he couldn't help but wanting to put a stop to everything. It's not just about juvia & lucy.