Please put my mind at rest

I am engaged to someone I have been with for 5 years. Early on in our relationship, I had a one night stand with someone else after a night out, something I feel very shameful of. I messaged the woman afterwards on facebook to apologise and let her know that I couldn't see her again as I was seeing someone else. I have since never heard from her other than a reply at the time abusing me for cheating. Absent mindedly going through my messages on facebook recently, I clicked on her profile (we are not FB friends) to find a picture of a newborn baby posted on her first birthday. The date of birth would tie up exactly with when I slept with the woman. There is a separate picture on the profile of the girl looking 3-4 years old. I have been going out of my mind looking into traits and whether they're dominant/recessive. I have brown hair and brown eyes, oval face and almond shaped eyes, all of which I understand to be dominant, though I know about carrying recessive genes. The little girl has very blonde hair, blue eyes, more of a square face and round eyes. Am I driving myself insane for no reason? This woman could have contacted me and never did. I know she is on a low income so would definitely need assistance financially. She also has one older child. Thanks.

Thanks Susie, that is helpful to see some sane words. I don't know, curiosity I suppose, wrong I know.