Mya - sounds like an interesting discussion with Bob. Cool that you're able to talk about this stuff, get some clarity of where each of you is coming from
rory - I have similar experiences to this, I think, often triggered by my failure in other areas (not relationships) but it flows on. I want to be whole-hearted in what I am doing, but inevitably I need to cull/prioritise the things in my life so I have enough energy for everything.
When I'm juggling things, and I feel like I'm dropping some of the balls, I feel like I need to stop, reassess myself, and restart. I can't just keep going with the next thing and the next thing. If the "next thing" is quality time with a partner, even if there's no particular issues between me and them, I might not feel like hanging out with them. I want the option of 'me' time instead, or first, or whatever. Even a short time. And I may not even need that.
It's just that, if there's a commitment to do something else, and I feel like I'm not altogether right with my own shit, I would like the option to break that commitment. It's a weird thing to have to say. It's like you need time out from being reliable.
Thing could be way off-base compared with how you're feeling. But at times like that, it helps when I'm with people who know me and the way I process. Their acceptance assures me I don't have to go into details when I need some space. I can just flag it, and take it, and I get what I need, and I'm back.
It can be hard, though, when you're all tangled up, to find the right words. I liked that 'spoons' article. A simple way for me to say what I feel, at times, could be: "I know have a commitment with you but I'm tumbling a little bit and I might need me time. Can I be unreliable and see how I feel?" If there's already a context of understanding around this, things can really be that simple.
Glad you're working on it, and hope you find a way through that makes sense to you. Recharging when you need it is so important! (Though I was intrigued by nycindie's take on things, above. A good counterpoint and something I will take on board too as a challenge to myself in those times)