Have you had any doctor appointments and ultrasounds?
I believe it was the 2nd guy who might be the father
It sounds more likely that the second guy is the father than the first guy, but your earliest ultrasound suggests you conceived on or around May 12 +/- 5 days, so that does not rule out the first guy entirely. In your shoes I would go through the pregnancy assuming guy 2 is the father, but would definitely get a paternity test with both guys once the baby is born.