you could try acting natural and not flirt with him.
Ask around, or confront him
What happens is, you confront him, & if he cheating then you'll know what to do.
maybe
I would confront the girl or warn your boyfriend
Your boyfriend is probably not ready for an exclusive relationship. If you don't think that he will change his mind, you may need to find another boyfriend.
Well if you really want to do something about it you really only have to choices: 1:confront the girl 2:confront the guy also know that what you may some girls consider as flirting is really guys just trying to boost their ego in a way like=okay i have a girlfriend but that doesnt mean i cant still be the guy i used to be. my opinion anyways :)
If you are secure in your relationship with your boyfriend, don't worry about it. It's okay for guys to have other friends that are girls.
Just confront him about it in a calmly matter
It's not a bad thing. Honestly most girls get jealous when there boyfriend is talking to another girl. But you shouldn't worry about it.
Confront to him that you don't like that. If he stop that means he values you, if he doesn't stop then you guys need to sit down and have a long talk.
Confront Him with the problem and if he does not, in your opinion, honestly answer, then you should probably find a boyfriend that doesn't lie.
Sometimes, girls can like 2 people at once or they could secretly like you, but are being pressured to date another person.