Maybe you could involve your self in "their" lives. After all, she doesn't come alone, she is part of a unit and you are part of a unit, being a unit together is the next step after working out a schedule. Really though, this is what you signed up for. If its not enough and you as a monogamous person then I suggest you find someone that is dedicated to just coupledom. Its not fair to her that this be an issue you expect to have worked out. If just won't be. Time management and lack of time are just how it is. If you are not willing to let her go then find something to do that fulfils you. Don't make her responsible for your happiness, she isn't, you are. You are an independent person, regardless of what you decide this is so.