Wow, reading your post, I was like, is this me?! I really identify with the suddenly realizing your friends are users and becoming burnt out after working insane hours but still wondering if it is me or the job.

As someone who DID quit her job, I have finally come to the conclusion that the problem is both me and the job. I am bad at setting boundaries, both with friends and with work. When someone asks me to do something, I feel like I have to justify saying no on some strange platonic level. I treat yes as the default. Sooner or later I resent all my yeses.

If you like your career path but not the job, change the job. Stop working the insane hours. Tell them they need to hire someone else. Ask them what they will do if you get sick. Figure out how you can split your job into two so they can hire another part time person to do the work.

When you stand up for yourself in these kinds of situations, you have a very good chance of getting what you want. They will not fire you - you are not easily replaced. Many workers have commitments that simply do not allow them to be available 24/7.

But, really -- figure out what would make you happy in the job you have and try to change the job to meet those requirements.