What do you do?
Many beginners check-call here, afraid of the flush....
...and this is a HUGE mistake. Think about it: if the villain has a King, he more than likely will just check behind, as he knows you didn't fire each street with complete air. If he hit his flush, however, he'll bet and your call is basically akin to throwing money away.
Bet-folding is a much better line for you to take. If he has a King, he probably will call and you win a nice pot. If he has a flush, he'll raise and you can get away from your hand. The net result is a higher EV play for you.
Check-calling is a useful tool when you're doing things like bluff catching. But when you're in a way-ahead/way-behind situation, bet-folding is more often the right play.
In other poker news, I just signed up for the annual WRPGT "Glaciers" tournament-by-email event. I really enjoy this yearly MTT, and I highly encourage all-y'all to consider playing in it. Best of all, it's free to enter. Here's the sign-up link: http://www.wrgpt.org/
All-in for now...