In a relationship with this girl for a while. Other girls in my extended social circle know this, but two flirt heavily to the point where I could escalate when we are out drinking. Only reason I don't is worry of backlash. Any experience with this?

How do I deal with the whole "I just hooked up with you but you have a girlfriend" line after? Or "Why can you be in a relationship with her but not with me?"

Any ideas on how I can spin them?