She teases you about it.

That night, Heather casually brings it up as the two of you are going to bed.

"Relax, honey, it's just blowjobs! I'm definitely not going to let him fuck me!"

"J-just blowjobs?!"

"Yep, no more than what your tiny willy is getting from me. And we both know Henry's giant logs deserves more than that!"

"But you're his mother!!"

"I'll stop blowing him once he moves out or gets a girlfriend."

At this point, your mobile phone rings, caller ID reveals it's Ms. K. You know better than to not answer.