Ex girlfriend moving in with her 2 month old?

So she's been having problems paying her bills and her "boyfriend" left her and the baby because he said he didn't want to be with her anymore. And we'd been raising my niece and daughter together up until 9 months ago when she told me she cheated on me and was pregnant and I ended things right there it was way too much for me at the moment, and last night she moved in with me and the kids and she slept with me and I told her I was still in love with her and I missed her. The only reason I broke up with her was because she got pregnant that was the ultimate betrayal to me, but I have a soft spot for kids I love my daughters to death and I have just as much love towards whitney. I want to make this work I really do....i