Your sister is pregnant, it is up to her to figure out where she is going to go with this very big commitment.

You need to slow down and think about how you are going to move forward even if it means that it will change your living arrangements. You had your sister as a room mate and while it has been a challenge for you to maintain that place to for you to live, you have also learned that it is easier to get by for you when you "share" expenses. So, if your sister has to change her lifestyle which might mean you need to move out, then you need to find another arangement where you are sharing expenses with someone else. People actually do this all the time, they can't afford to have an appartment on their own so they find a room mate to share with. Also a big trend that has taken hold is that people are buying their own homes and having an apartment set up in the home to help pay for the mortgage instead of just paying someone elses mortgage. So finding ways to be "independent" is a process and many people learn to build on that process and it is not unusual for parents to help with that effort either.

I do agree that your sister should be on more solid ground before having a child however.
IMHO, it is better to have a "commited" healthy relationship established before planning to bring a child into the world, which is a very long time and expensive commitment.

OE