Robert being so cavalier about infidelity, since he has always been such an avid practitioner, is an interesting offset to the other two. Pinter hasn't created him that way for a callous, uncaring contrast to the two illicit lovers. No, Robert clearly loves his wife, just as he is close to his friend. What's implied is that he measures his caring for both of them with his tolerance for what society considers their "betrayal." Pinter is establishing his strength of character by indulging them and wanting them to be happy.
Robert's tolerance is a conscious decision, not an act of disdain. When he discovered, on a vacation in Venice, that Jerry had been sending Emma letters, he is initially jealous and upset, but his anger quickly cools into sarcastic humor. There is an unspoken concern over his being the father of their son, but he is quickly assured and still trusts her enough to accept her word. The three actors all do well, but Conte's work is the most impressive. Robert requires quite a delicate balancing act.
At one point, Robert says he is turning down a novel focused on betrayal because "there's not much more to say about it." Pinter's cleverly intelligent play shows that to be a lie.
, Harold Pinter, betrayal