Trying to catch my bf?

A couple months ago i found out my bf was being flirty and snap chatting a lot of girls. I don’t have the best trust in him and i really dont know what to do because I don’t want to break up with him, but I’m getting these feelings that he’s still doing his shit. So I’m planning on getting a text free number and pretend to be someone else and flirt and see what he does. If he continues the flirting then I’m done. Should I do that or should I get a Snapchat instead. I just don’t know what to do anymore