Keeping the red line up

As I review my games that I played so far, I realised that my red line has been trending slightly negatively over the past few sessions I had. I reasoned that it could be due to lots of missed opportunities to steal pot and folding a lot of pots uncontested.

Therefore, in my session today, I tried to be more conscious of folding too easily and unnecessarily. I think it is important for my winrate to spot opportunities to float and bluff some pots. 

So, with my increased post flop aggression, I managed to keep my red line up and at the same time, have a solid showdown winning. The drawback? I played few hands per hour as I am involved in more post flop plays. 

Well, obviously, my good run helps. Not until towards the end of my session where I lost a big pot to a fish who completely caught me by surprise how passive he plays this hand. 

He was lucky that I have the nut flush and I couldn't really put him on any hand based on the way he play this hand. If I had anything worst than the nut flush, I would have checked river and he earn peanuts. Sometimes, fishes are dangerous because they are so unpredictable. 

Poker Stars, $0.10/$0.25 No Limit Hold'em Cash, 9 Players

BTN: $18.80 (75.2 bb)
SB: $30.91 (123.6 bb)
BB: $12.74 (51 bb)
UTG+1: $31.34 (125.4 bb)
UTG+2: $23.28 (93.1 bb)
MP1: $25.25 (101 bb)
MP2: $25 (100 bb)
Hero (MP3): $25.31 (101.2 bb)
CO: $22.74 (91 bb)

Preflop: Hero is MP3 with K K
4 folds, Hero raises to $0.75, 2 folds, SB calls $0.65, BB folds

Flop: ($1.75) 5 J 2 (2 players)
SB checks, Hero bets $1, SB calls $1

Turn: ($3.75) A (2 players)
SB checks, Hero checks

River: ($3.75) J (2 players)
SB checks, Hero bets $3, SB raises to $29.16 and is all-in, Hero calls $20.56 and is all-in

Results: $50.87 pot ($2 rake)
Final Board: 5 J 2 A J
SB showed J A and won $48.87 ($23.56 net)
Hero showed K K and lost (-$25.31 net)

As played, should I have folded this hand? I took quite a bit of time to think about this hand. I only lose to fullhouse now. Did he have it? I discounted that he has pocket 22, 55 as he is likely to reraise my flop bet on a drawish flop. I discounted JJ and AA as he is likely to 3 bet me preflop. My blind spot: I did not consider AJ which is in fact what he has.

My mistake perhaps but really, even if I consider that there is a possiblity that he has AJ, could I ever my nut flush here? I posted this hand at twoplustwo forum to seek opinion on this (Link below).

http://forumserver.twoplustwo.com/78/micro-stakes-full-ring/25nl-zoom-kk-nut-flush-hand-1190780/#post32490469