think of it this way.... you just admitted you've had your ex boyfriend in your pocket for 3 years dreaming of him and having sex with him.
If you had just had sex with an unknown guy it's atleast thought of as possibly HOPEFULLY someone nobody knows. Maybe you just met him and never want to see him again and regret it a lot. A guy or gal could hope that it was a one time MISTAKE.
I'd want to leave my man for just saying he's "thinking" of his ex, let alone has been for 3 years and that he just had sex with her!