No, I do not. I eat a balanced diet of veggies, beans, nuts, fruits, etc. I probably eat more of that than most people (although I have a serious weakness for french fries and beer). For B-12, I cook with nutritional yeast which has a lot of it. For protein I like to mix up servings of tofu. tempeh, seitan, beans, and nuts. Seems to cover me just fine. I'm in really good health for 42.
But who said I was in harmony with nature? The whole point about environmentalism is that we're overusing resources. Therefore, re-use, recycle, etc. But look, I do not view veganism as a religion. There's no vegan hell for people who occasionally deviate from the concepts. But as in recycling or CO2 mitigation, the idea is to identify areas that are wasteful and reduce those where possible. Eating meat is far more wasteful than eating veggies, so reducing or eliminating consumption of meat is better for the planet.
Very cool, Una, on not taking vitamin and mineral supplements. That's a pet peeve of mine, vegan or no. I AM in favor of folks taking these supplements in the spirit of them taking medicine - when they cannot obtain necessary elements from available food sources, or when a medical condition, an abnormality, applies a serious health stress. All cool with that. But the vast majority of vitamin and mineral supplement takers - well, let's just say the marketing strategy for said items has been an enormous success. It's marketing and nothing more.
Smart fishing is a nice hedge against gobbling up tracts of land (Herbert - she's got... HUGE... tracts of land!) for obtaining the complete protein and some of those lesser known items found, for example, in fish oil.
I wonder how much cow meat here in the USA is slaughtered for our beloved cats and doggies?
I sense that people here in the USA, however, are moving away from beef, very slowly. Keep hearing more and more how people are eating the dairy products, the eggs, the fish - and chicken.
I'm not a raging carnivore just as you're not a religio-vegan.

Difficult not to feel a bit uneasy seeing those cow eyes and knowing what's in store for it. My grandmother, who DID live on a farm (but I'm city folk) told us how she'd cry and cry when they took a cow away for slaughtering. She said they're like big dogs and you could easily grow attached to one, emotionally. It might be one of the reasons I eat very little beef? Maybe. I'd really be much more comfy if we ratcheted down their slaughter and the same for piggies. Or let them live out their lives fully - and then when they croaked on their own - we could make usage of their carcasses? Who the hell knows. That's a possible course of action.
It's a carryover of human empathy. "Right" or not, we haven't the same type of connection to a chicken, a lizard, a fish, a rat, a squab, a bunch of ants over which we coat chocolate. It's a human bias, that we "connect" to these larger mammals. I think many feel that way.