Marriage expectations are clear:  For better for worse, for richer for poorer, in sickness and in health, 'til death do you part.  Why would anyone agree to such a thing?  Children, family, and God's love for us.  My wife grew up in poverty and her parents remained married for 45 years until her dad died.  I grew up lower middle class, my parents were married for 50 years until my dad died.  We model our marriage on our parents, and it hasn't let us down yet, and, believe me, we have had more crap to deal with than most of the other people that we know.  This is our faith.

All this analysis is silly.  We plan and God laughs.  If you're going into marriage with any expectations, except the sheer will and desire to stay married and raise your kids, you're setting yourself up for failure.  The blessings of family and the presence of God are extraordinarily fulfilling.  The trick is to find a spouse that shares this understanding.  The trick for the Church is how to teach this.