Hey, come on OP, you're not failing any of us, we're just strangers on social media, who feel for you, and want you to be happy, which you're clearly not with this man who uses you, and abuses your love for him. Every time you try, it will become a bit clearer that he's just coming up with the same old excuses to make you stay, where HE'S comfortable! If he truly cared about and loved you in return, he would be making massive changes in his behaviour and mindset, in order to prove that he cares, so, if he keeps to his word this time, then all well and good, BUT, you've already told us, that even while he's talking the talk, he's also blaming you, for HIS mistakes, ie, he'd have walked the dog while you were ill, if only you'd asked - if he truly loved you, you wouldn't need to ask, as like my wonderful DH, he would already have predicted your needs, and done the job, never mind waiting to be asked, especially when you keep telling us that you don't think he'll allow you to take the dog if you leave, because the dog is HIS!!!
Here's an example of a man who truly loves his partner:
Due to my disability, I rarely manage more than 2 or 3 hours sleep at night, but by morning, have usually fallen into a deep sleep. My DH, and I sleep separately so that I don't disturb him with my constant tossing and turning, so when he gets up, usually a couple of hours before I do, he makes a point of leaving his phone in his room, so that if it should bleep, it doesn't disturb me. I didn't know this until a couple of days ago, when I heard his phone bleep in the distance while having my breakfast. I'd seen him run to answer it before, and wondered why he didn't just have it in his pocket, so asked why he keeps leaving it in his room, to which he said 'Well if it bleeps before I wake you with your breakfast, I don't want it to wake you up, do I?' A silly little thing you might think, but he knows how little sleep I get, and the fact that he's actually thought about this, absolutely amazes me, and shows me just how much he cares. THAT to me, is TRUE love!
So, my advice to you - Keep trying, the time WILL come, and I for one will still be here, rooting for you, and waiting for that one post that tells me that you've finally found your strength, and done what you really needed to do.
Keep the faith - you can do this!