If you are with a Sagittarius and they occasionally vanish into their own life — travel, projects, friends — that is not a signal of disinterest. It is oxygen. Sagittarius needs freedom like fire needs air, and a relationship that cages them will suffocate.
Here is the counterintuitive truth: the more freedom you give a Sagittarius, the more they choose you. They commit through wanting, not through obligation. If they stay, it is because being with you genuinely beats being free.
Own independence is the most attractive thing you can bring to a Sagittarius relationship.