Do I have a right to feel betrayed?

Long story short one of my best friends is a guy and he was dating this awful woman. A couple weeks ago he found he overnight at another guy's house, that is just the tip of the iceberg of everything he's found that she has done. He called me at 3am when he found this extremely distraught and came over to my house (I'm married husband is also friends with him) anyway it was a horrible week and he was extremely upset and it's been this way for a couple months now back and forth. He has caught her in numerous lies and has become extremely depressed. Well I find out yesterday that about 5 days after he was at my house at 3am he let her come over and stay the night. She is extremely manipulative to him. The fact that he let her come over and stay the night after everything is infuriating and feels like a betrayal. Am I allowed to feel this way?

Do I have a right to feel betrayed?
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