Hi there,
I was diagnosed two years ago and I'm still honeymooning. For me it's a blessing and a curse as my needs seem to change from week to week! That might also be something to do with my age/being a woman though!
The only way to tell if it's coming to an end is that insulin needs will increase, so just a case of monitoring really.
The better the control, the longer the honeymoon can be according to my DSN. So if I were you, I'd make sure I switched to sugar free drinks for example and if he's having something very high carb, then monitor him closely, and inject if he's climbing.
I'm on roughly 7 units of background (I'm on a pump now) and I inject on average 1 unit for 20g of carb. This week it's not been working so well, and I've had to increase the ratio, next week, I might have to drop it.
That's my experience of the honeymoon, I think mine is definitely on it's way out.