Currently, the pair of them are going through the painful process of 're-evaluating their relationship'. One of you might see it as a prelude to marriage, while the other might see it as the biggest commitment they're ever going to make. Talking to each other beforehand about what moving in really means to you is crucial. You may find that your partner doesn't seem to get the same treatment from members of your family that married partners get. Adding gravitas to your relationship can be tricky when you've got rather limited terms to refer to the love of your life.
Married people can talk easily about their 'wife' or 'husband'.
Mike and Sarah certainly got their wires crossed when he moved into her flat. After much debate, the couple have worked out a schedule which allows each of them to do their own thing on some nights, but reserves certain other nights for them as a couple. How much you want to share and do together and how much you want to keep your own space. If you're moving into your partner's home, then it's only common sense on your part to get the property put in your joint names before too long. If you're buying together, then you should formalise your share in the property, ideally owning it as 'joint tenants' so that you would get half the proceeds in the event of you splitting up, or so the property automatically passes to you should your partner die.