He is outdrawing you and you will lose no matter what as long as that happens. He is paying way to much for his hands. With AK you will win 2/3 of the time so your best bet is to get as much money in up front as you can. With the flop that came off I would have bet 1/2 pot and 2/3 of the time it's a fold, he hit a six it happens. 8x the bb is a good amount based on having no knowledge of the table myself, sometimes you want to limp and hope for a steal and push, sometimes you can get 20x the pot. The problem I see is he is not folding to your semi bluffs. So don't semibluff. He bluffed you out of a pot, showed it. And then did some real damage with the fullhouse. You did have an openended straight draw at the the flop with middle pair, i think you overbet it vs calling.

I would try to act tilted, ie limp in often and try to catch him with a big hand. But try dropping the semi bluffs.