re: Does your non-married significant other split living expenses 50/50 with you?

Let her pay 50% of what she pays now. Living together in his house will thus help her financially. It will help him too, because he'll start getting these contributions from her. They both win.

She's taking the big risk here, moving into a house he owns and has control over. He could kick her out, etc. Ultimately, living together, being together every night, etc., will make or break this couple.