Common situation in Stud/8

[Nick_Foxx]

let's say you have a respectable high hand such as split queens or jacks, which is an overcard to the board... you complete and get the pot heads up with someone showing a 7 or 8 (not the bring-in)... on 4th street, you catch a blank and your opponent catches an Ace

what do you do if he bets? what about if he checks?
what about on 5th street if he catches another low card while you do not improve? (his board may be something like 8A2)

mike