She is!

Unbeknownst to you, as Heather hangs up on your phone all to her about cancelling, she gets a text.

Checking her phone, Heather cracks a mischievous smile as she reads it; "Meeting with John?"

She texts a reply; "No. Come over."

The text is innocent enough on the surface, but Heather knows it's a invitation to fucking. She takes care of her make-up as she waits. The knock at the backdoor five minutes later is all she needs. Opening it up, she lets in her secret lover for a night of sex. The person she fucks instead of you, her piece on the side...