What does it mean that a guy I am hooking up with doesn’t care I bang his friend?

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I used too hook up very causal with this guy and it end about two years ago. Now drunkly I hooked up with one of best friends. It happened again last weekend and he told me that he knows I used to hook up with his friend And he doesn’t care. Just wants thoughts on this. Be kind!
What does it mean that a guy I am hooking up with doesn’t care I bang his friend?
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