Quit, but don't be a dick about it. Say that you won't be able to come in anymore, that you're grateful for the opportunity and learned a lot, and all that good stuff. If he asks, say you've been working on other projects and they've gotten to a point where you can no longer commit the hours to his lab. Usually good if you're doing something on the side (volunteering, independent research, working) that he knows about, and you can say you took on additional roles/were promoted/whatever.
Definitely don't be a queen of drama.
Do have other things going on on the side.