I'm thinking of getting in a relationship very well knowing I won't want to spend a lifetime with them.
That's interesting. Why don't you want to spend a lifetime with them?
I know they would only be a troublemaker, longterm.
Relationships don't all have to last forever but you should be on the same page when it comes to the relationship. If you want a short relationship you should be honest with them to avoid hurt feelings later on.
I don't want a long-term commitment and I want to keep it that way.
That's perfectly normal, lots of people never want to get married. You just need to have a frank conversation with your partner and you might find out that you are both on the same page. There's nothing wrong with two adults having fun.