Does Marriage Make People Happier?

Yes, but only if the marriage is a good one. Bad marriages make people miserable:

people in self-assessed poor marriages are fairly miserable, and much less happy than unmarried people, and people in self-assessed good marriages are even more happy than the literature reports. We also find that the results differ importantly between women and men, with members of the former sex showing a greater range of responses to marriage quality than do men. A final set of results is that, when marriage quality is controlled for, the apparent marriage effects on other outcome variables, such as self reported health and trust, change significantly.

It is amusing that this confirms the received wisdom about marriage, that men always think things are fine.