Am I the asshole??

6

AITA for not wanting to share my inheritance with my sister after she stole my girlfriend?

So I'll keep this brief, me (29M) and my sister (30F) had a falling out when she had a long ongoing relationship with my girlfriend back when were in high school 12 years ago. My Ex-girlfriend was in the closet and said she had a longtime crush on my sister and was using me to try and get close to her. My sister had been out to my father, (Our mom died years ago in a car accident) who was doing his best to be supportive to her but was struggling. I would like to mention my dad always had an issue with cheating in a relationship and had told me that if I ever cheated on my girlfriend at the time he would disown me.

Now one day I did walk in on my sister and my girlfriend 'going at it' and was heartbroken. They tried to explain to me they were sorry about what happened, and my sister seemed remorseful but said the two of them had strong feelings for each other, but I didn't want to hear it and I just left after breaking up with my girlfriend, mostly since I just wanted the last word. Now at dinner my father could see I was upset and asked me, and given how upset I was I just blurted out what happened. He was beyond pissed at my sister and yelled at her for breaking my trust and trying to justify it. My sister tried to defend herself by pointing out how hard it is to find any girls willing to date her given how conservative our area is. However he wouldn't hear it and kept shouting at her. When she graduated high school she left the house, and I later learned she was disowned.

My sister believed that he disowned her because she was gay and was just using the situation to have an excuse for himself. She stated she wanted nothing to do with him either. She did still stay with my ex and their relationship did go further and my ex supported her through the whole thing. They even got engaged last year.

Now cut to the present. My father recently died due to some complications with cancer. My sister didn't bother to go to his funeral and I hadn't spoken to her in years. I had heard from one of my aunts she was struggling financially. Now when it came time to read the will my father left most of the money to me, with a very small amount for my sister so she wouldn't contest the will. I want to mention, the amount he left to me, it's in the low 8 digits.

My sister was furious when she found out and then found out I wasn't going to share it with her. She said it was unfair since our father was being homophobic and I was supporting it. She accused me of having a grudge over what happened in highschool, and I can't deny I was bit upset about that. It left me feeling distrustful of any future partners and hesitant to even try being in a relationship for years.

My aunt pointed out that if I kept this grudge then I would lose any possible relationship with my sister, to which I snapped back an insinuated she would just try and steal any future girlfriend I get. Which I do sort of regret.

I just want to hear from all of you, AITA?