Limit MTT hand

[Big Limpin']

OK, i make no secret that i suck at limit.
Anyways, hand went like this:

-Hero BB, 78o
-Several limps, hero checks
-Flop 578 rainbow
-SB leads out, hero raises, table flolds, SB calls
-Turn 9. SB leads out.
-Hero fold(?)

Can i be that sure that i am 4outer based solely on his "suspicious" betting? I feel like he probably has the str8, but, how sure do i have to be to drop the hand? Well, i know how to figure that out, i mean, how sure would YOU be that you are beat?

As the hand played, i folded pretty quick, then spent the next little while 2nd guessing. Was this a bad fold?

THanks, and remember to dumb down answers so non-limit guy can understand

Oh, should say, was from 40+4 limit MTT.
I'd guess this is ~equivalent to 2/4 (?) for villain skills
Also, very early in game, stacks are inconsequential

BL' knows this is the STT forum, takes risk of being moderator-[censored]