[9cao]

I will guess that SB slow-played his 55 and the BB has Ace of spades.

You played it fine. The only interesting part was the river since if the SB is rational, he can only call with a boat when you go all-in. If you just called the BB's bet instead, he could call you with just Ace of spades and probably raise you with a boat anyways. Might have been better +EV play. Nice hand.

Edit: Missed the straight-flush potential. Much more interesting now.