That would piss me off to a ridiculous level. I know we're all meant to be alpha in here but that stuff gets on your nerves for a reason. It's instinct. And you, as a hot-blooded male, are right to react. The mere fact you said he was high-value means he was passively AMOGing you.
Don't be AFC and whine to your girlfriend about it, it's your inner insecurities causing it. Ignore them as best you can and deal with this high value male like every other one.
Being more fun, romantic, spontaneous, exciting and brave around your girlfriend is good advice too.

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I believe in fate and karma. Both are forces of immense power, but do you know what else is?

You are.

I don't know, its known that the guy she was flirting with is in love with a other girl that we know.

My gf even told me on text when we talked about it jokingly ''Haha so cute he is in love with ***** the one with the **** '' like that

Surprise her - that's the whole point. Tell her you have a surprise for her and she has to wait to find out what it is. Maybe even bring a picnic along and have dinner/wine on the beach. She'll be like pudding in your hands. Or putty. Not sure how that saying goes.