Personally, I am wondering why she's been your girlfriend for 4 years, what 37 when she met you, you have an ex-wife, you live separately and she goes to bed around 9pm weeknights and you can't stay over, you have to leave so she can go to sleep.
After 4 years?
Did your wife cheat on you? Were/are you really in a committed relationship to start with?
I'd be engaged at least therefore in the knowing that I mean something serious to you. And, you'd be staying over as well on some occasions where is the bond here?
Perhaps reality is, she is "just a girlfriend" at 41 years of age, tick, tick, tick do either of you want kids? She's already peri menopausal.
I'd seriously consider what you have to start with and perhaps what she "may" feel she's been missing out on.