One of the earliest red flags was the warning from my co-workers when they found out that I was planning on going out on a date with XWH. My co-workers told me that XWH was trouble and to stay away from him.
Looking back, XWH was very elusive about what he was doing and who he was spending time with whenever we weren't around each other. My red flag should have been that he really did not want to share his life with me. What little I did find out, other people would tell me in passing or I had to pry just to find that out. Since I worked a lot and was a single mother at the time, I shrugged it off and trusted him to tell me what he wanted me to know whenever he was ready for me to know it. But that never happened and he went to great lengths to keep me isolated so that I could not meet any of his friends outside of my sister and one of his roommates. But even back then, there was a total double standard on this because he expected to know where I was and who I was with, but hid it behind a veil of concern for my well-being.
Red flag that XWH started taking up more and more of my spare time when I wasn't at work. Anytime I wanted to hang out with any of my friends, he wanted to come along or he would suddenly have something really cool that he wanted me to go do with him. That was not a coincidence as he sought to strain my friendships and isolate me from any sources of support or to isolate me from any version of events that wasn't his own crazy making mind games. But it was so subtle that I totally missed it until he became my only friend and only person to hang out with.
The biggest red flag that I blew right past was how XWH trash talked his exes. If I had listened carefully, I would have realized that he was telling me many of his abusive expectations and double standards as I was getting to know him while also testing me on whether or not I would call him out for how full of shit he was. XWH blamed all of his financial problems on his ex-wife and his former roommate. There was a tiny element of truth in his claims, but not enough to explain away the extreme financial jam he was in.
XWH also talked at great length about the tiny infractions that his exes committed that (according to him) gave him legitimate grounds to cheat on them, stay out all night, steal something from them, etc. All of these infractions centered around his exes hanging out with other people and not allowing him to keep them isolated. With his first girlfriend, he bragged about throwing her out as punishment for hanging out with a co-worker and not coming straight home after she got off of work. She had to move in with the co-worker because she had nowhere else to go.
With his ex-wife, he bragged about cheating on her as punishment because she chose to hang out with her classmates (she was still in high school when they married). With his ex-girlfriend before me, he punished her by cheating on her with her frienemy in retaliation for him not being invited to her birthday party. The list of stories goes on and on, but the underlying message was that he expected total devotion from his partners and any failure to revolve your world around what he wanted and to be at his beckon call at all times resulted in him punishing them.
So now, I pay a lot of attention to anyone who blames someone else for how they conduct themselves or that brags about getting even with anyone for anything or even about any hint of an expectation that others have to do what they want. I will pay attention to those red flags now.