Is it normal for my mom to be uncomfortably close with my partners dad?

My partner (22M)and I (21F)have been together for over 5 years, we’re a long-time and very close couple. The entire time my mother (Christine, 52F)and his father (Mike, 54M) have had what I would describe as an inappropriate relationship, mostly because my boyfriend and I got together first. Neither of them will acknowledge this flirty behavior and get wildly defensive when called out. For nearly the entirety of my partner and I’s relationship, our parents have been on the phone with each other 24/7. Theyre constantly in connections and constantly flirting. Christine has never had boundaries in this sort of sense and seems to think flirting his harmless, while often times Mike plays stupid and flirts with her back. I also want to note that most, nearly all, of this flirting is initiated by my mother Christine who clearly has had a looooong time crush on Mike. (And this is some pretty uncomfortable and suggestive flirting.) Since the start of my partner and I’s relationship, Christine left her husband (my dad) and moved concerningly close to Mike. It wasn’t long until my partners parents got divorced too. Its pretty obvious to me that Mike and his wife got divorced because my mom Christine simply would not leave Mike alone. My partner and I are extremely tired of this and we wish our parents had a more normal relationship…but we can’t tell if we are being dramatic or reading into things too deeply. Is it normal for our parents to have this close of a relationship?