His ex girlfriend is pregnant, but he has not told me yet...?

[Drue]

Background: I am 18 he is 19. I have been dating him for a little bit less than a month now, but things have been going really good. I like him and I he seems to really like me. We text whenever he is not at work and I am not in class and talk on the phone for at least an hour each day. We see each other two days out o the week on avg.

Situation: When I first met him people were telling me he was engaged. I looked him up on Instagram and Facebook and found him and his supposed fiancé. I confronted him about it and the both updated their stuff to no longer engaged. They changed their profiles from them together to just themselves(except one she originally changed then changed back). Anyways, while making sure that this was not bullshit and that they really, honestly we not engaged I came across undeniable information that she is pregnant with his child. He has yet to tell me about it and I am wondering what do you think it means?

1. How long is appropriate to wait for someone to tell someone this? Please note that he makes it seem like he REALLY likes me. We have also both opened up to each other A LOT.
2. Should I mention that I know and how would you recommend I go about that. At this age I just never feel the urge to ask someone if they have kids.
3. Do you have any other advice for this situation?
Thanks for reading and answering.
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@Kayla Oh he definitely knows. People were congratulating her everywhere for it. It is not on the DL.
@Innogen thanks I am pretty sure that is what is going on. Lying by omission. I just never been in this kind of situation, so I did not know how much time was allowed. He lied out of omission before I think. Like when I asked him if he was engaged he said no. Then a week later when I confronted him about it and said that his facebook and instagram said he was not lying because I never asked if he was EVER engaged. Well maybe that is something you should just mention huh?