When you become co-dependent, how do you deal with the change in routine? How do you learn to think about "me" instead of "us?"

Find your own interests. Sometimes people in relationships, or even children with their parents, and I've seen this with friends. You do everything together and share everything with that person. But you are an individual, you have your own likes, dislikes, preferences. When there's a break in routine, don't take it personal, don't panic, take it as an opportunity to locate the "single" you. Spend sometime time alone, take a walk, read a book, meditate. But the goal is to find your personality and identify your strength and weaknesses. That way, any change that comes your way you're not left wondering "how are WE going to handle this" but instead you will search for ways that YOU yourself are able to handle the change without changing yourself.