Need support. Badly.

I had my baby girl 3 weeks ago and I just found out that my fiancé brought drugs into the house (and has been doing them) It was a huge fight and he left. I'm guessing for the night... I don't know. Anyways, I know I need to leave and call it quits and be the best mom I can be for my daughter. It sucks, I never planned or thought of being a single mom. I was going to be a stay at home mom and home school. Everything I thought and knew was a lie and my heart is crushed. I know I need to to what's best for my daughter but the first step is so hard. Leaving. Any single moms out there that can tell me how they did it. What's the hardest part, does it get better, how if and when does Dad see baby, talk to you, how is the relationship between you and the child (if child is older) is it lonely - not for you but for the child. Like setting a dinner table for 2 instead of 3. Little things like that.
 Thanks - one crushed and heartbroken Mama