TRUE!
The FL and ML are two different individuals. Since the ML worried about his niece and took care of her as a parent, I'm guessing that he has a strong parental instinct and probably that's what's making him wanna take responsibility for his unplanned baby and subsequently is trying to get on good terms with the FL too.
In FL's case, her backstory is more than enough for the readers to understand her actions.
Everyone needs to have some patience and let this story mould beautifully! Personally, I feel that both our leads have parental insticts and want to do their best for the unplanned baby and for this they both need to be on good terms. And for this, they need to build a healthy relationship and for which they need TIME!
I guess the author will slowly and gracefully build up a relationship between both the leads as the story evolves AND EVERYONE NEEDS TO BE PATIENT INSTEAD OF NITPICKING EITHER OF THE CHARACTERS ACTIONS!

Damn all of guys are so judgy. Give mc a break...if I grew up in the kind of environment she did and had divorced parents (+a distant mom), then I'd end up just as guarded as her. Plus, we may know ML is the one she'll end up with but she herself doesn't know so she's right to be sus of his intentions #-.-)
He is a stranger to her in every way. They literally only had a 1 night stand and the baby wasn't planned. The reaction to him is pretty realistic. Some of y'all r such naive romantics smh