A partner has to be going somewhere too
Your Sun burns Sagittarius-style from the 7th house, which means you become yourself alongside somebody who has their own direction. A partner without a project of their own eventually feels like an anchor rather than a companion. You need a relationship between two people who are each already moving.
That requirement gets stated badly and often too late. Said early it sounds like a warning; said in year four it sounds like an exit. Say it at the beginning, plainly, as a description of how you work.
Honesty arrives before tact does
In close relationships you say the true thing quickly, including the unflattering one, and you assume the same is welcome in return. For some people this is an enormous relief after years of being managed. For others it lands as carelessness. Establish which you are dealing with early, because the same sentence is a gift to one and an injury to the other.
The freedom clause, stated out loud
What you need is not distance but the absence of a fence: the trip taken without a negotiation, the friendship that is yours, the evening nobody has to account for. Unstated, that need gets taken by force and looks like unreliability. Named as a term of the arrangement, it is easy to grant and most partners are relieved to know the rule.
Drawn to somebody from somewhere else
Difference of background, country, field or worldview attracts you strongly, because a partner who sees things differently keeps the conversation alive. That works while the difference is interesting and gets harder when it becomes logistics: whose family, whose country, whose assumptions about money. Do the practical conversation early, while it is still theoretical.
Staying without feeling enclosed
The pattern to watch is leaving good relationships out of restlessness rather than dissatisfaction, and calling it honesty afterwards. Before you go, ask whether anything is actually wrong or whether you are simply due a change. If it is the second, change something else instead and stay, and find out what the fifth year is like.
Told the truth, and expected to hear it
What makes a relationship work for you is the absence of management: no hints, no atmosphere, nothing you have to interpret. Say that this is what you want and ask for it explicitly. Then hold up your end when the truth being told is about you, which is the part that tests the whole arrangement.
A partner with the opposite temperament
In business you do best paired with somebody methodical who finishes what you begin, and you will find that person mildly irritating for the first two years. That irritation is the point. Write down who decides what before you start trading, because your instinct is to move first and explain afterwards, and that is exactly what a methodical partner cannot tolerate.
One person at a time, and then a crowd
You are drawn into people quickly and can be a considerable presence in somebody's life for a season before the attention moves. Some of them experienced that as a friendship being formed. Be honest about your own pattern, and keep the handful you actually intend to know for decades in separate, deliberate contact.
Their family, at a distance
You will take a partner's relatives cheerfully and lightly, and where they expect a closer involvement your friendliness gets read as indifference. Ask your partner what is actually expected rather than assuming your version travels. A little formality early, offered rather than demanded, buys you decades of being welcome in that family without ever being absorbed into it.
Freedom is not the opposite of commitment
The assumption underneath a lot of your leaving is that staying means being reduced, and it is worth testing rather than believing. Commit to something for a fixed long period and observe what actually happens to you. The evidence is the only thing that settles this, and it takes years rather than arguments.