I've never hit triple-digit happiness. Ever.
Why? Well, if you have anywhere near that much happiness (even just 30 to 40 happiness), it's usually a good time to go on the warpath, or to expand.
100 happiness, to me, is sort of like the Panzerscharfenator General achieve for having 100 units in a single game (and spawned 100 generals and won 100 games across a life time): if you have 100 units, well, you probably were capable of ending the game a long ways before you reached 100.
This is the best advice. Happiness is much easier at lower levels.play settler level.