You’re info is too sketchy. Do you mean a Tzedaka meshulach, a very emotionally needy person, a mentally ill guy who keeps coming to your door, a shidduch that you don’t want? What?
No one has the right to tell you, however well-intentioned, that you should just let the person come around because it’s your extra mitzvah. I am in the same situation with several different such people, because I try to always be friendly to everyone I meet, and some interpret that as a sign on my head saying, “This is the sucker you have been waiting for to dump your tzoros on.”
I have ended up with people who are VERY, VERY emotionally needy calling me up to cry every day, even late at night. The first several times I was empathetic to their pain and even tried to give them sound beneficial advice (which they never took, anyway) to help their situation. But it is emotionally exhausting and no longer a mitzvah when you have other crises in your own life to deal with, and their problems are weighing you down.
This might sound mean to some, and I sincerely don’t mean to be, but you cannot be everyone’s best bud, and you cannot solve everyone’s tzoros, or be responsible for their happiness. Always be a good person, but you have to be able to distance yourself sometimes. If they call, screen the calls, if they show up at your door, either do not be home, or actually go out and tell them you have an appointment. Eventually they will find another person, they always do.