Right and it's also about respect. If you continue to let people flirt with your SO even if you trust them and know they won't cheat, your letting the person straight up disrespect you.
How can you say you my man's friend and sending him hearts and kiss faces knowing he got a girl. Would she be cool with another girl sending her man that? No.
I felt disrespected by that and if I keep letting it slide simply because I know he won't cheat, it still doesn't change how I feel
And if she a real friend to him she be like "my bad bruh" but if she ain't then I'll see that and handle it accordingly.