I think you need to step back, perhaps with the help of a family therapist, and trace your own motivations (often unconscious motivations) for parenting the way you have. There are reasons why you currently find yourself exploited, used, angry, and sad. What else is going on in your life that gives you feelings of competence, self-worth, and a sense of purpose? It's time you stopped giving to these kids in a manner that allows them to disappoint you with their selfishness. They need to hear from you how you genuinely feel about your relationship with them. It shouldn't involve blaming them anymore than it should involve blaming yourself. Seeing a therapist can give you a life and family perspective you are not currently capable of giving yourself. It can help you to take back the power you have given your teens to define who you are and what you are worth. You need these burdens and this grief lifted from your soul. Please take action.
Parent Feels Unappreciated
Toddler and Teenager Expert Advice from Carleton Kendrick, Ed.M., LCSW