<human>: Can you succinctly summarize the text in 1-3 sentences?

The relationship I'm in is a dead end and I've decided that I need to shut it down and move on with my life. 

However, this one is a bit tricky. Previously, I haven't been very engaged with the girls I've dated, and leaving was done pretty much overnight. Almost always it's ended with us not being friends anymore, primarily since I never give a good enough reason for breaking up. 

This time it's different however. The girl I'm with is extremely manipulating and I am a big pushover nice-guy. In short; we own an apartment and a dog together, so I can't just pack up and leave like before. 

Relationship-masters of Reddit; How do I end a relationship gracefully like a mature adult? 

Backstory: 
The problem I'm having is that I don't really have a good reason to give her that won't be offensive to her. The core problem (or cancer) of the relationship is her lack of interest in me, and the fact that she uses me to supplicate her every need. I have to go shopping because she can't carry the shopping bags, I have to walk the dog because she is tired / sick / feet hurt / headache / whatever, She gets to decide whenever we're having sex, and whenever we do, which is eyebrow-risening seldom, it's a big bucket of boredom. I also do all the cooking, primarily because she sucks at it, but secondary because she wringles her way out of it. She's been using me for her every desire while giving me absolutely nothing in return and it's simply gone far enough. 

However.. If I ask her: "Are you happy in the relationship?", her reply will of course be "Yes, of course i am". She has no reason not to be. If she asks me and i say anything of the reasons above.. well, then she has all kinds of great ways to make me feel guilty about myself.
<bot>: Girlfriend is having the time of her life, I'm miserable as fuck. I need some suggestions on how to end it gracefully.