[tinkerman]

Currently, what are your options. You need an ace, 3, 5, 6 or a 7 to improve. We have seen an ace go and as such you have 19 outs. There are currently, 41 unknown cards.

For you to catch good on 6th is 19/41= 46%. So you fold if you catch bad. Hence lose a BB 54% of the time.

To catch good on 7th your chances are 18/40 = 45%.

As an approximation, I assume he has the same odds for catching good on 6th and 7th. He'll made a made hand less than an 9 20% of the time and beat you when you catch good twice.

So you are making a made 8 20% of the time and will even lose this 20% of the time. So you win the pot plus (3BB)16% and lose 3BB 4%.

The next scenario is you catch good then bad. You will lose if he makes a good 9. Which he will make 70% of the time. Meaning you lose probably 2BB (maybe 3BB).

The final option is you catch good and bad and your opponent catches doesn't make his 9. Here I assume the expect return is half the pot since you'll win half and lose half of these situations.

Summarising the odds as follows:
54% of time lose 1BB
16% win pot plus 3BB
4% lose 3BB
18% lose 2BB
8% win half pot

This gives an expected return of 0.2 pot - 0.54BB so the pot needs to be 2.65BB to be neutral expectation.

This feels low to me, so maybe I have made a simple miss calculation. Can you spot it as I can't.

If this is right, then you should have called.