Will a man stay with a woman and save money for a period of time if he is planning to leave her and how will you know this is the case?

Yes, some men are crass enough to use a woman to save money. It wasn't a secret that for many years young doctors pulled this off while going to medical school and as soon as they became full-fledged doctors and got their practice going they dropped the woman that helped them. If he has his money in his own account and doesn't share expenses then you can bet he's using you. If he doesn't talk about his future with you and that both of you are working towards a that future then he's using you. He should pay half the expenses and not expect you to work and put all your money into his future or safe his own money and give you nothing in return. If this is the case have a talk to him and tell him you aren't willing to continue on with these arrangements any longer.