Am I overreacting

My husband has been fairly social recently, going out a lot and one particular womans name has been coming up a lot. I dont really know her but I know my husband has known her for a number of years. Not well but she has been around on and off. She the recently sent my husband a video of herself singing him a random song and wishing him a good day. It was via his Social Media account and he showed me to prove I have nothing to worry about but my question is why the hell would this random person send him a video?? What level of conversation are they having for her to think its ok to do so? It seemed very flirty and I told him I am suspicious. He acted super nervous shortly afterwards when we went out together and she appeared. Problem is my husband is a serial cheater. He has a history of stepping out of our relationship in various ways and also often engages in "microcheating". Am I overreacting?