Well, then, you really are going to need a DNA test. If the second guy's pre-ejaculate did contain sperm (and at this late date is impossible to know that answer) then both men's sperm would be in your system on your projected ovulation date. If your boyfriend often finished inside you he has the edge, but it only takes one sperm. I'm sorry it is not more clear.
Did the doctor or ultrasound tech on June 18 give you an estimated due date? It would say EDD on your chart.
Actually I get an ultrasound on Jun 18 but I just figured it was wrong since I couldn't remember my lmp
But my crl said I was 8w6d
On aug 21 I got an ultrasound saying I am 19 weeks and 1 day . I've never gotten an early ultrasound.
Just from the facts that you give, it is possible that you got pregnant by guy 2, but it would be helpful to know more than just when your last period began. Did you get an early ultrasound? Do you have a due date given to you by a doctor? Was it based on an ultrasound or just a little wheel or a chart?