It's hard to build up trust with someone new, especially when you've been burned in the past. It hurts even more when it involves a member of your own family. In today's 'Am I the A$$hole?' post, OP told us about how he caught his high school girlfriend cheating on him with his sister, which left him with long-term trust issues. It's one thing to be cheated on, but it's a whole 'nother thing when a family member cheated you. If you can't trust immediate family members, then who can you trust?! The two siblings ended up not being in touch until their father passed away. Apparently, OP got most of the inheritance because their father was upset about his sister's cheating, but the sister believes that it was because he was homophobic. Now, she expects OP to share his inheritance money with her. Scroll down to read the full story.
This is already a huge betrayal on OP's girlfriend part, and it's even worse that his sister was involved in the cheating scandal.
Dad has the right attitude about cheating. It's never a good idea.