It is time to take a big sigh of relieve. It is not the other guy's baby.
* You had sex with him during your infertile window.
* You had a 5 day period after you had sex with him.
Your due date puts your conception date at around June 27. That will mean sex between June 22 and June 28 got you pregnant.
Congratulations and take care. And STOP worrying!