Eight weeks three days from July 8th brings us to September 5th, so that computes. The ovulation that started this pregnancy would have been 14 days after the period began, July 22nd on a 28 day cycle. That ties in nicely with your July 22nd encounter and the fact that your sex drive was high that day. As long as you did not have sex with your ex after July 16th (cycle day 8) you can be pretty sure your fiance is the father.
You went to the hospital a few weeks ago, and they told you at that time that you were 8 weeks 3 days? Or if it was a few weeks ago, they told you some lesser number than 8 weeks 3 days? What was the date of the hospital visit, and did you have an ultrasound, and what due date did they give you if you had an ultrasound then?