I was up against a villain who i know played tight not always aggressive but i know he would have a top hand here is what happened .5/.10 game
I had 5d 6h i bet .30 standard starting bet button called and bb called
flop came Qd 9D 4s we all check
turn comes 7d bb checks i bet .45 hoping everyone folds due to low cards because both players are very tight bb calls
river is 8d i get the striaght but also there is the 4 card flush
i have the one diamond i know the villain has all high cards and if he has a flush he will win bb bets i hoping he is bluffing go all in for 3.00 and he calls and has Ad qs just like i thought what would have have done would you have called knowing he could be bluffing or could have the nuts or would you have done what i done hoping he was bluffing but only fooling yourself into thinking he was bluffing when you know already he was not. God I can't just go with my guts and know that I just can't win every hand. I was doing good I got to learn to control myself

BB shove the river OOP while check/calling previous street with 4 diamonds on the table, it should not been that hard to fold there

*i misread BB river bet, sorry. calling is fine if you think hes bluffing there, shoving is unnecessary
also when i play under rolled i cant think clearly under pressure, never play above your bankroll

So on the river the BB leads out and you decide to raise all in over the top?
If that is what happened you should just call on the river rather than raising all in.
If the BB open shoves then it's an easy fold with a 4 card flush on the board.

fold pre

dont open preflop

I would have given up the pre-flop hand, it's a marginal hand that I do not even play in cash game final positions.

The flop had to bet more. I think so. The enemy just waited for his card

yeah I couldn't open preflop there with that hand there now maybe if it was suited and Iwas in late position then maybe I would but that hand I wouldn't not offsuited 56 no way no how you don't have straight and flush outs even though you did hit your flush there you hit a four flush board which killed your chance because like you said he was a nit and more then likely had the A of diamonds and did have it in the end when he called. Poker is all about odds and outs and maths and you have to take that into consideration when play which a lot of people don't they try to get tricky and do plays with all kinds of hands that are -EV when you should be playing only +EV hands and let the fish play the -EV hands you will find your bankroll and your tourney runs go deeper if you just play +EV hands and situations yes you will get sucked out from time to time but hey that is poker but in the long run you will be a poker winner if you stick to the +EV situations you will see it let the fish play tricky you play right.

There could also be a 6d for the straight flush. When we see the opponent go all in and you see 4 diamonds on board, the most possible is the excistance of a flush or a straight flush in this situation. If he didn't have something strong, the most possible is to make a good bet to comfuse you. I would fold in frond of this, because there are other possible much stronger hands which can win.

You have to respect the flush draw there (and also draws to a better straight). 3 cards of the same suit on the board should be making you cautious to an extent, when there are 4 you usually need to shut down and try to get to showdown very cheaply, preferably without investing anything else, unless you have top flush or better yourself.

As played, betting the turn in position is not entirely horrible with your open ended straight as you have fold equity too, but that is a dangerous looking board and I think checking it might be wiser. You don't always have to make those sorts of bets to try and take down the pot, sometimes you just have to be more restrained. You're up against potential flushes/draws and better straights/draws. Even against a tight player they potentially have quite a lot of hands they could call with in the BB that are connecting with that board and already have you beat, or are drawing to plenty of outs that will beat you on the river. Maybe a C bet on the flop would have been a better option, making use of the fact you are the aggressor and in position. You can be a bit less concerned about board texture for your C betting if you have position against a single villain.

All that said, there is no way I open 56o unless I have two massive nits in the blinds who are never fighting back against a steal over at decent sized hand history, if not more. Opening garbage hands leads to tough post flop decisions that you are better off without. Steal with something that has a bit more potential.

The GODS got you from the beginning. You shouldn't play 5-6 even when suited unless your not expecting to win then its to show you bluff so they bet you later when you have good hole cards.

you played against tight not always aggressive player way would you think he will bluff in that spot then ?

I'm surprised you bet with 5d 6h pre-flop. In my opinion, here is the main reason for the lost hand