I suck at this game, posting to get any logic flaws out of my head.

7 Card Stud High-Low ($0.25/$0.50), Ante $0.05 (converter)

3rd Street - (1.40 SB)
A lot of my low pair outs are gone, which makes chasing a low better I guess.
Seat 2: xx xx 3___folds
Seat 3: xx xx 3___bets
Hero: 7 5 3___calls
Seat 5: xx xx 7___folds
Seat 6: xx xx A___calls
Seat 7: xx xx 6___folds
Seat 8: xx xx J___folds

4th Street - (4.40 SB)
Seat 6 looks like he's going high. Seat 3 might be going low, but I definitely have the best low draw out of the bunch. So I gotta call, right?Seat 3: xx xx 3 9___calls
Hero: 7 5 3 2___calls
Seat 6: xx xx A A___bets

5th Street - (3.70 BB)
Seat 3, who might have been the only remote competition for the low, hasn't gotten any better there. Seat 6 was going high last street, so he has to be going high this street (I have a verrry strong feeling this is flawed thinking). Therefore, I have the best low draw and should continue. I've also got a pair, so I can outdraw the aces still (I had forgotten that a chunk of my low two pair outs had been burned on 3rd).
Seat 3: xx xx 3 9 9___calls
Hero: 7 5 3 2 5___calls
Seat 6: xx xx A A 4___bets

6th Street - (6.70 BB)
Got the low now, gotta charge seat 3 if he's still trying to get there
Seat 3: xx xx 3 9 9 6___checks___calls
Hero: 7 5 3 2 5 8___bets
Seat 6: xx xx A A 4 T___checks___folds

River - (8.70 BB)
My board reeks of a low. I dont think there's any fold equity in a river bet, being that he's likely to call me down with just one pair of nines. Better check it.Seat 3: xx xx 3 9 9 6 xx___checks
Hero: 7 5 3 2 5 8 K___checks

Total pot: (8.70 BB)

Some people say complete 3rd. I think calling in this spot is ok with other potential lows behind you. On 4th, you need to raise. You've picked up the best low draw. If seat 3 was going low, you need to trap him for the bet(s) here. Just because you don't have a made hand doesn't mean you can't raise it. You're a favorite to take 1/2 the pot. If you and seat 6 just bet each other through the rest of the hand, you lose money on each one of those bets because of the rake, assuming that you take low and he takes high. This is why you need to raise it here and catch seat 3 for bets. 5th is definately flawed thinking. First, you don't know that 6 is going high. The power of the A in any hi/lo game is that it is the mecca for both high and low. The way he played this hand so far is consistent w/ him starting w/ 3 low, then making AA. That's a monster hand in Stud/8. If this is the case, he now has 4 to a low that may beat you, and a high hand that is a huge favorite. You need to charge him for drawing to that low (if he has it), but also charge 3 because, frankly, he has little business in the hand. It's way to easy for him to be beat, and even if he has the best hand w/ 2 pr, 6 has a lot of outs to outdraw. But, because he has shown a willingness to throw money away, hit him hard. You should be raising here also, because even though you haven't, it looks like you made your low. 6th is good. Looks like the AA were going low, although I wtf'd when I saw he folded. Now 3 had to call, because he has the best high. I suspect 3 was looking for low also, so I like the check on the river.

While you have the best low draw, I don't think you can raise an open pair of AA in a split game with your hand. If you were open ended with live cards, raise all day, but you will NEVER be ahead for the high on 5th and while getting extra money in the pot with seat three having bricked and called a bet, I think it's just wasteful. It looked good now because the AA folded later in the hand, but I think it's kind of a bad play to raise with no immediate high outs and the low not locked up. I am all for building a pot with a good low draw, but I really don't think you can do it against two aces. 99% of the time, you won't find him folding them anyway.

But to the OP as wlel, I wouldn't try to put the guy with the Ace as going either high or low, he could have 42 in the hole, he could have a pair, or any reasonable low cards. A pair of aces with two babies is a pretty strong hand, mainly cuz of the AA but also the low potential.

i cant understand the check on 4th if you were going to reraise on 5th as a jam

If you want to get better at Stud 8 listen to Paul Darden on Cash plays on pokerroad.com. Very good interview and lots of insite. He gives some pretty specific examples of hands that belong in the muck that lots of donks play.