Don't expect marriage to make you happy or to make your life easier. Relationships exist to teach us to love, which is the most challenging skill we develop as humans. Don't let unhappiness or the hard work of marriage be a barometer of whether your relationship is working.
Always look for what there is to stay for.
I have been married 25 years this spring and have four kids ages 10-20. I also own Good Clean Love and write and teach about making love sustainable which keeps me honest in my day to day relationships.