Self-discipline as been described as being willing to defer immediate pleasure for long-term gain.
You may not be fond of what you're presently doing whether it be a job or courses in college but if you deem it to be a prerequisite for realizing your dreams you'll press on to complete those tasks.
However with regard to mate selection each of us (chooses) our own friends, lovers, and spouse. We get to determine who we will spend our time with. It makes little sense to invest a lot of time being in an unhappy relationship. If one is unhappy in relationship and chooses to stay then (they) are choosing to be unhappy.
Our lives for the most part are the end result of the chooses and decisions (we) have made along the way. Each of us is responsible for our own happiness!