In the early stages, it can be easy to overlook red flags.
Say you're both on two decent incomes, no kids, not living together yet, it's easy for someone to put on an act doing the whole 'wooing' thing.
One way I've learned to get bad ones to 'show their hand' earlier is to slow down the romantic fantasy by 'switching the dream environment' a bit.
So suggest an activity where its not just 'doing something nice that HE likes'.
Express something authentic about a genuine situation where you're unhappy, or where YOU found something inconvenient or made you upset.
That ALWAYS seems to trigger the "bad ones" into a very 'Real Him' reaction.
They actually get really disproportionately angry at the idea that you're not just going to operate as a cog in giving him a perfect life?
They want to create a life where THEIR thoughts and feelings and moods dominate.
So they really, really hate it if their new girlfriend acts as anything other than a permanently smiling, Madonna like oasis of calm and support.
Eg: me: "there's hassle on the train, I got some really rude comments from some yobs
"
Abusers reaction formerly Mr Polite, but now along the lines of
"you are NOT upset! you SHOULD not be upset. You should HANDLE it yourself. You should deal with it. what about MY feelings? I wanted a NICE night out/date. you're too OVEREMOTIONAL. I solve PROBLEMS, because I'm a MAN. why are you being NEEDY and a PRINCESS and RUINING everything? you're just like ALL THE OTHER WOMEN. I had a RIGHT to a NICE NIGHT OUT and now you've RUINED it."
Subtext: your emotional 'job' is to dance round my every little whim and make ME feel good. And if you have an authentic emotion of your own, my plan is fucked. Why aren't YOU looking after ME?