I'm not going to tell people I'm in a relationship
And why do you not want to tell people that?
Because I don't want to tell the whole world that I'm in a relationship.
It is within your right to to keep your private life private. Not everyone needs to know who you're dating, and most of them won't even care. You should just keep this information to people who would appreciate it.
Okay but I will tell them the moment I get bored of my partner. It's just a test run to see how they react.
Testing people is not good so you can just keep it to yourself until you feel ready to share with others. It is understandable to want to keep somethings private.