Question about the first story

Okay when the boyfriend was going underwater to get the keys out the dead husband's pocket...we clearly see the husband come alive and supposely choke the boyfriend and I assume he kills him but when the wife shoots through the door thinking an intruder or whatever was trying to get her..it end up being the boyfriend she kills but didnt the husband already kill the boyfriend underwater??? How did he end up making it back to the house ALIVE? That ending confused me.