Yes, people can go for years, even forever, without getting symptoms. As many as 90% of people who have genital herpes don't know it because they don't get symptoms or they get symptoms but don't recognise them as being herpes. I had it for years before I realised that my symptoms were herpes.
Once a person knows they have it (or in your case, when their partner starts showing signs of it), they might realise they've had symptoms all along but just never thought they "were anything." So it's possible that your bf had discounted his symptoms as being "nothing to worry about" until your outbreaks put a different "spin" on them.
It's also possible that your outbreaks (OBs) became transmitted to a new location on him where he'd never had OBs before, although I suspect it may be more likely that he's just interpretting the symptoms differently now. But it's possible he might have it in a different location (e.g., orally, especially if what you have is HSV-1 rather than HSV-2), which then got transmitted to your genital area, which then got transmitted back to him in HIS genital area. I hope that makes sense.
You should both be tested, if you haven't already. Get a swab test taken within 24-48 hours of the first signs of an outbreak, for best chances for an accurate result. Just be aware that a negative result isn't always accurate. A blood test will tell you IF you have it, just not where you have it.
Let us know how you make out.