@Ali0Pose,
I've spent a large portion of my life contemplating break-up ethics and have developed a thorough philosophy concerning break-ups. I read a great deal of Aristotle, Aquinas, Locke, and legal theories to develop my philosophy. In fact, my major paper for my doctorate was on the subject of breaking up.
In my view, it is unethical for you to break-up with your boyfriend. There are 2 reasons for this. First and foremost, you would be breaching a contract. All relationships are contracts. It's simply that our modern democracy has chosen not to enforce those contracts. But most certainly, a moral contract exists nonetheless. At a minimum, a relationship is a quasi-contract or a contract implied-in-fact.
A contract exists whenever you have a quid pro quo bargained-for exchange. In the case of a relationship the parties contract love in exchange for love. This creates a moral obligation because both parties sacrifice something trusting that the opposing party will fulfill their end of the bargain.
By leaving your boyfriend, you breach contract. And this is a great moral wrong. This is just like a business contract. If a distributor asked a supplier to build a factory to make dolls and then that distributor pulled out of the contract, that distributor would most certainly be sued in court for millions of dollars. Love is even more valuable than products in a business deal. Your love is worth millions to your boyfriend.
You entered the relationship. If you breach that relationship, you violate natural law.
There's a second reason why a break-up would be wrong - but we can get to that later.