Baby Daddy?

Ok so I am like two days into playing sims 4 and have lots to learn yet. But my sim tried for baby with her boyfriend but the next day woohooed with her roommate. At some point she realizes she is pregnant, but how could I know who the daddy was before she had it and I looked at the family tree? Also when the roommate asked the date it was due, I was sure the sh t woud hit the fan. But no he seemed pleased enough and married her before the baby came. I though maybe it was his. But after the baby was born and I see the family tree, it is not the new hubbies though he still does not seem to know that, or maybe he just does not care. He was really upset when he saw her flirt with the baby daddy back before the pregnancy was known, but not that it is not his? Help me understand please.