Collecting Payment

My sister had a car accident and needed her car repaired; her car was the only vehicle in the accident. I repaired her car for her, she owed for parts and my time. The parts weren't hard to get from the wrecking yard and repainting them to match her was a breeze. But it took a week to do everything needed. Of course, she didn't have the cash to pay me back even for the parts or paint. But she offered me sex as payment and we worked out an agreement of the number of fucks. Then she dropped the bombshell, she was still a virgin, I could only fuck her ass or get blowjobs. It was one of my dreams to fuck a woman ass, I've had a fair of sex with women and have had blowjobs and straight sex. None of them were willing to let me fuck their ass, I would have done for half what we agreed if she had known. So, I fucked her ass for 3 weeks and best part no condoms needed. I filled her ass with cum every time.