At what point do you throw away A high flush on non-paired board?

[frozenhops]

Sorry for the messy conversion, but here is the setup.

Important Stacks:
Hero $85
Villian $45

In CO w/ A [img]/images/graemlins/heart.gif[/img] J [img]/images/graemlins/spade.gif[/img]

I raise to $2 pf, BB calls.

(Pot $4) Flop J [img]/images/graemlins/heart.gif[/img] 9 [img]/images/graemlins/heart.gif[/img] 2 [img]/images/graemlins/heart.gif[/img]

check, I bet $2, BB calls

(Pot $8) Turn 7 [img]/images/graemlins/heart.gif[/img]

BB Bets out $4, I call, hoping to trap

(Pot $16) River 8 [img]/images/graemlins/heart.gif[/img]

BB goes Insta-allin for about $37 more. My roomate is standing behind me, I felt there was a large chance that he had the 10 [img]/images/graemlins/heart.gif[/img] , my roomate felt like I was a huge pansy for not insta-calling. I ended up calling anyhow after deciding he has to have the straight flush 60% of the time just to make this -EV

The beat doesn't bother me, but I have been trying to think of how deep the stacks would have to be before I folded this hand, if ever. If the pot is $10, and the overbet is $50, or $100 do you throw this hand away? Or should you always call because he needs to show you the straigh flush over 50% of the time.

The answer changes, somewhat i'm assuming, if there is actually 2 cards that give straight flushes out there? Any insight or discussion would be very helpful, thanks.