[ChipsAhoya]

I imagine he paired his five and thinks you paired your ace so now he's betting w/ a J to your Q and the best (although he doesn't know that for sure and/or may not think that...) draw. As played I think you have to C/R here and c/c the river. I mean, he COULD be slowplaying 5th but I doubt it since a bet would not get you to fold since you could have a 6 draw even if the A did pair you; therefore, he chooses to take the free card. If you had the 8 up, you may fold to a bet drawing almost dead, so a made 7 would probably want you to "catch up" on the next card, so a paired 5 would be much less likely to slowplay here.

Weird spot, this is a great hand. I thought it was going to be be like one of my steal hands where it always goes:

xx6Q8Jx
vs.
98237J2

and of course I have to keep betting every street and of course I get called down and he makes his 8...

-ChipsAhoya