You are not wrong. At least totally. But if you knew before the party that she was a lesbian and that she was likely to get frisky with you, you should have clung to him tightly. As it is, you are pretty enough to have her flirt with you. Quite an accomplishment. I would agree that he is a lucky man, but you said that you are lucky as well. It’s always a good idea to apologize if you’ve ever upset anyone, much less someone you love. I hope you already have. Because what you have in him will be almost impossible to replicate. Don’t wait for him to be the first.
I would caution you to never withhold intimacy even in cases like this. Never use it as a weapon. Sure it won’t be “awesome”, but guys don’t react well to being turned away. You may have lost a part of him you will never get back. Ask me how I know!