I wouldn't keep a bottle open that long. A good malt does wane and will likely have some problems developing 6-8 months out from being opened. Granted most people don't know what they are, but opening and holding isn't suggested by the truly educated unless the bottles are subject to a preservation system.
Thus, I might suggest something you've not thought about: Buy 10 bottles. Open one each anniversary and drink it by the time the next anniversary roles around. One thing is a definite: Your relationship will evolve the same as your whisky drinking and you wouldn't want a stale whisky ten years from now the same way you don't want a stale mate.
Buy single cask whiskies as they will be as unique as your mate will hopefully become, and over the years you will simply not be able to replace those bottles.
Like I tell people about my wife, when I met her and she decided to allow me to call her my wife, I was a 100 point wine in her eyes. After two years of marriage I was 95 points. We celebrate our 7th anniversary this year and I'm now down to 89 points. However, I am still able to convince her that I will be getting better with age.
Anyway, you might choose a smattering of 10 year whiskies, and as time goes by you might look for vintage bottlings from the year of your marriage. Remember, you marriage will be a journey the same as your whisky exploration.