My bet would be on the ex. If you use an online due date/conception date calculator, it says you likely conceived around October 26th. Only way to know for sure is a test when the baby arrives.
Hi, I don't suppose I have to tell you by now that pulling out is not a "method" of anything, unless you count it as a method of guys getting their own way about not using condoms. I do hope you got tested for STDs.
If you are due on July 19, the conception calculator says:
First day of last menstrual period: October 12, 2012
Probable date of ovulation: October 26, 2012
Possible dates of conception: October 22 to October 30, 2012
Due date: July 19, 2013 (40 weeks)
This would lead to the possible conclusion that your ex is the dad, but it is not foolproof, since there are only three days between Guy A and the first possible conception date. A conception calculator is only as good as the method by which you got your due date -- was it by ultrasound? How early was the ultrasound in the pregnancy? (The earlier the more accurate, and the later, well, if it was past the first trimester, it could easily be off by 3 days.)