This happened to me last week.
After being with my boyf for almost 20 months/going to uni soon i started to think "hmmmmmm, do i want to get around a bit? I was really confused about what to do.
But then i experienced a metophorical cold shower and thought "shizzle, if i leave this relationship i will have no life left, no best friend, no comfort, (no chauffeur lol) and kinda snapped out of the mood. I think i mistook "settled" for "boredom".
Its all good now though.