What should you do if your girlfriend of one and a half years was going to move in with you but now says she wants to get her own place but stay together?

Combining living spaces is a hard step to take. It's easy to fall into the comfort of having someone there when you come home, but the thought of the permanent nature of this arrangement can make people hesitate.

You have been together 12 years, so she obviously likes you. Loves you, even. As long as you're still spending time together there is no reason to move in together. Keeping separate living spaces is healthy and lets each of you create your own personal world. Somewhere that you can retreat to in order to collect yourself. I know couples that live together but have separate bedrooms for that very reason. Of course, they spend their nights together in one or the other's room. But, they still have their own room for their own space.

Don't worry about it unless she stops spending time with you. This is the most clear indication that she wants to stop the relationship. However, if she is honest about staying together then you have little to worry about.