Yes this situation is possible, HSV-1 is really common and most people have no symptoms, people can have HSV passed to them by partners who never knew they had it.
I am not sure if I fully understand the second part of your question so let me know if I answer it wrong. Most people who get HSV do not know it has been passed to them, if someone does get symptoms they will get outbreaks from time to time. Someone can pass HSV easily when they have an outbreak as there is lots of virus in the sore.
It’s possible for HSV to still pass when someone is not having an outbreak as the virus will shed from time to time. This happens because every now and then the virus will travel up the nerve to the skin (dry or wet skin), it may only be shedding for a short period of time. As the person will get no symptoms during this time they do not know it is happening.
Given the above it’s possible to be with a person who has HSV and does not know it for years and never have it pass to you. It can certainly happen out of nowhere, when you have been together for several years and you just happen to have sex when your partner is shedding HSV. Maybe your skin is a bit fragile from something like a razor burn or maybe sex went on for a bit of time so the skin has small micro tears and the HSV is there from the shedding and is able to get into your body.
Let us know if this did not answer your question or if you have any more questions or concerns.