I have had this happen twice with married men unfortunately. First guy was on Tinder who claimed to be divorced. Claimed he didn't have social media, claimed he worked weekends and only had one weekday off but it always changed, and I noticed his pictures on Tinder were very old and fuzzy. Eventually, I researched him and found out he was still married.
Second guy was a co-worker who claimed he and his wife were no longer in love, they lived in separate bedrooms, and she no longer slept with him. Eventually, we became close friends and he admitted to me they were married but they were both just massive cheaters. Ugh.