thank you for this link. I have a question: after i've login my nemwallet with my trezor, in the future i can access my nem wallet only with my trezor?
Correct. That's the idea.
If Trezor disappears or you lose yours and can't afford another one you can get a private key from the Trezor seed with this -
https://github.com/saleemrashid/nem-trezor-standalone but obviously only do that if absolutely necessary and only on a very, very offline computer.
And then you can restore your XEM by opening a conventional private key nano wallet with that private key. There might be a nano seed wallet sometime, but there's no mention of it yet.