Fantasy about adopted sister?

Me and my sister are adopted but almost from birth. We had sexual moments when we were younger but no real sex. She's now married and I have a wonderful girlfriend. I'm now 53 and she is nearly 50. Issue is I still fantasise about having sex with her because I'm sure it would be amazing? I kind of feel guilty about my feelings but don't know what to do with them? I did once make her a proposition when I was 27, but she was with a boyfriend and not interested. Trouble is deep down I think she's got the hots for me? What do I do? Do I tell her about my horniness, or do I go to my grave silent?
Fantasy about adopted sister?
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