Are you married? Is she your betrothed? Did you commit to each other? Did you express you want to be the only one for her? Did she accept? You falling for someone does not automatically make them exclusive to you.
Also, what seems to be flirting to some people is just showing kindness to others. Smiling, laughing, engaging in conversation, kissing on the cheeks may be normal in some cultures and not in others. I “flirt” with strangers who I will never see again, someone who held the elevator doors for me, someone who was sitting next to me in public transportation, or someone who was just kind. Just a tad bit friendlier than being civil. It makes people’s day. In reality, it has been 3 years since I was involved with someone in any way. Is she really flirting, going out of her way to see them, get all pretty with makeup and dresses to meet them, giving them opportunities to make a step towards her, or is she just being social?
If there is something that makes you uncomfortable about her behavior and you wish to have a more exclusive relationship, you need to make the commitment. Both of you. If she is going to give up her not necessarily romantic social interactions for you, you have no right to “ignore” her. If her needs, including attention, are more than what you are willing to give, and your demands are too much for her, it is not going to work. This is how relationships are built.