I agree that the "flush of love" that people talk about at the beginning of a relationship doesn't last - you can't sustain that level of excitement once you get to know someone and especially once you're sharing the same space.
After writing about the negative aspects of the Army, one of the positives that comes with frequent separation is the way it can sustain a relationship and make it feel fresh again. A six month tour is a hard slog both for the person on ops and the person left at home to carry the can. However, how many women nowadays get old-fashioned love letters? I do. My husband and I exchange "blueys" regularly when he's away and there's something about expressing your feelings in ink and paper that makes you think about those feelings and the person you direct them towards.
There's definitely a "butterfly feeling" when he comes home again - despite the need to adjust to living together once again. Obviously as we have a young family, real life does bite, but spending so much time apart really makes you focus on what you do with the time you do spend together. So, while it's not that flush of new love, it's certainly not mundane or routine for us. I definitely don't take him for granted and I know he feels the same about me - he simply couldn't do the job he does if I were not at home doing what I do.
It is difficult when they're away to explain and rationalise things to the children - they miss their father desperately and can be upset when he misses something important to them. As they get older, it's been harder to shield them from the reality of Daddy does for a living - Afghanistan/Syria/Iraq etc are a constant news presence.
Anyway, my point is that not everyone loses all of that "new love" feeling - it is inevitable that things change as we grow older and move on with life/children/family/work etc - but it is entirely possible to keep a measure of excitement and freshness in a longterm relationship (my husband and I have been together for a little under 18 years).
Maybe the uniform helps...