My advice is to stop feeling guilty. What's done is done and the only way now is foward.
1. you've ended a relationship which needed ending. Good for you. Now, I know the ex would do anything to keep you and she together - but honestly, it sounds like she'd need to change sooo much. And which such a huge change required, I doubt she could maintain it. Keep your distance and allow yourself the space required to get over her.
Forgive me if I've missed it in this thread, but are you still supporting your ex? Because she doesn't work and won't do what's required take care of herself, I suspect you may be. Do you need assistance is trying to extricate yourself from her life? If so, what are the difficulties you face?
2. sounds like the new girl is fond of you and I wish you the best. It's not impossible for things to work, but keep an open mind that this woman may be a stepping stone while you move on. Try not to get too attached too quickly. Take time to see how things pan out.
good luck
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.