Am I tripping??

So my best friend and the guy i’m messing around with (also who im like in love) and i all hang out sometimes. Lately i’ve been noticing little things and i dont know if im just crazy. The other night we all went out and afterwards we went out to eat. At the restaurant i told her to switch seats with me so i could sit next to him and she just gave me a look and stayed there. After that she kept (in my mind) flirting with him by pretending to put ketchup on him and put her hands on him in “subtle” ways. She also kept saying some suggestive things towards him that i had peeped and commented on. She has a baby daddy who she’s still messing around with and so in love with, but she’s still flirting around with my guy? I dont know whether or not i should say or do something because i dont know if im just overreacting or going crazy?

ps, that night wasnt the only night things like that have happened, it was just the most that i’ve seen.