Brother & Sister Getting Too Close

Your sister and her husband have been having financial issues so you offered for them to come and stay with you and your wife while they get back on their feet. She tells you how grateful she is for helping them out and is practically giddy that she's finally going to get to spend more time with you again. You've always been extremely close, but since you moved away, you don't see her nearly as often as you'd like. Things seem to be going well, until you bump into her in the kitchen in the middle of the night. Neither of your partners are happy about the arrangement and it's caused tension in your relationships, so you find yourselves seeking solace in one another...