You've related a one sided story about your aunt. I'm sorry I didn't hear any marital details that you may be privy to? How your uncle feels? Intimate details about their married life? About the feelings of the other woman? What drove the issues surrounding the affair? Financial? Social? Sexual? Psychological? Childhood insecurities Etc. The list goes on & on!

Sorry I did not hear any reason for a judgement except your emotions.
There are deeper issues in a marriage & an affair that you nor anyone else are exposed to. It's between them.

People have a public life, a private life and a secret life.

We just don't know every detail to stand back & point fingers.