I am pretty new to hold e'm, I've been playing with my friends for a couple of months, mostly just for fun with no money. When I play one on one with one of my friends, a thing that stings me alot is that he goes fishing all the time. Like the other day the flop was 6AA, and i didnt have anything on the board, and he ends up checking all the way to the river, then when I raised him he reraised me and it turns out he had another A. He always does shit like that, and I'm not sure how I can stop falling for it. How can I distinguish between when he is not aggressive because his hand is weak or because he is fishing? Or how can I otherwise lose less frequently to this style?

thanks