Help setting boundaries with flirtatious ex ?

Not even sure if this is the proper sub to ask this but recently my ex has become seemingly more and more flirtatious. She wasn’t doing this when she first moved out but the past few months it has started with quick phone calls regarding our son that would turn into 20 minute convos completely unrelated to coparenting that she would abruptly end. During drop offs/pick ups she’s usually standoffish but now whenever she isn’t with her new partner her demeanor has completely changed. She will get up close and personal with me and try to have convos unrelated to our son. She’ll compliment me, weirdly smile at me, and just try to set a flirtatious vibe in general. I realize looking back the phone calls are on me as I could have simply hung up and should have but I think apart of me enjoyed talking to her, but how do I deal with her doing this in person? It’s not that that I necessarily dislike the flirting as I’ve engaged with it a bit but I think I want it to end for my own emotional health. I don’t know what her intentions are but I’m not confrontational and don’t want to cause conflict or upset her. And I especially don’t want my son to see or hear anything that could confuse him any further than our separation already has.