I was born in the United States, but I was educated in Canada, which mostly follows British English spelling (or at least did when I was a student). Nonetheless, we were constantly exposed to American spellings through books and other US publications.
When I was an undergraduate in Toronto, I noticed American spellings blended in with conventional British ones in many newspaper and magazine articles. In addition, Canadians seem to prefer spelling verbs like "analyze" with a "z" rather than an "s." I had American professors who would correct all of my Canadian spellings and Canadian professors who would correct all my American spellings.
I spent eight years living in the United States in my thirties, and for six of those years I was a secondary school English teacher. This meant I had to learn proper US spelling myself first. So neighbour became neighbor, centre became center, and travelling became traveling.
After eight years in America, I moved back to Canada where I continued working as a high school teacher. Guess what? I had to forget all the American spelling rules and reacquaint myself with the Canadian/Brit system again. Neighbor became neighbour again, but analyze was just fine as it was.
To top it all off, I spent nearly a year living and working in England where I had to learn the proper British system of spelling for the first time in my life. Analyse was most certainly not analyze there, thank you very much.
I now live in Hungary, and I have noticed that I tend to stick to American spelling most of the time, but occasional British/Canadian spellings of words still manage to slip in here and there, leaving me with a blended kind of English that appears to be all my own.
I love English, and I have made the English language the core of my life, but with all its inherent trickery, it might very well be the devil's language of choice!