Here's the thing about being a Sagittarius in a relationship- we are known for being loyal and adventurous. We are the only sign which has both of these qualities; every other sign possesses only one.
When we get in deep enough, I think it's just the sheer idea of not being able to see an exit sign from where we're sitting that terrifies us.
We're also known for expecting too much from people, and then getting bored when they don't meet our expectations. I read things like this and think it sounds pretty spot on, and then I think... goodness, what a pain in the ass.
They say Sagittarians are really only meant for each other. Sometimes I think that's true, and then other times I don't know how there would ever be room for two of me in a relationship. I'd probably run away.
I think the most someone like me can really hope for is to find a person who, instead of needing to escape from me, will escape with me.