When Oliver talks to Charles the wrestler, it is part of his plan to get rid of his brother Orlando.
Specifically, he tells (or warns) Charles that Orlando will take revenge on Charles if Charles defeats him in the wrestling match. He says Orlando will stop at nothing -- he'll even try to poison Charles. So Oliver says that Charles had might as well kill Orlando.
This conversation takes place after Charles has come to tell Oliver that he will be wrestling harder than usual. He says it is his love for Oliver that has made him say this -- he wants Oliver to tell Orlando not to come and wrestle so he won't be badly hurt.