So...who's the father? My money's on the boyfriend. I really really want it to be Barney, but it just didn't seem like enough time has past for her to know and it be Barney's. I really hope this isn't the last episode for 6-8 weeks, but I figure it probably is.
I think it could easily be Barney's. Do we know for sure how much time has passed since the last episode? Unless I'm missing something there's no reason to say it couldn't have been a couple weeks ago.
Besides, even if it's the boyfriend's baby, Robin and he could break up anyway because of Robin cheating on him and Barney could simply be the baby's stepfather - we learned already, that blood relation doesn't seem that important to him when it comes to babies; especially since he appears to sincerely be in love with Robin.
There's lots of different ways this storyline could play out.