The ending only bothered me for a short time, now it makes a lot of sense to me.
I think watching it the first time you get so wrapped up in omg they are really going to get married and live happily ever afterness that you think is happening, only to feel like it is pulled out from under you, that it is hard not to get upset initially.
But once you take a step back, calm down, stop being a drama queen, you realize it certainly isn't an ending for them, it is just the ending of the show, and in the context of the show, the ending makes sense.