when you are married
No. You give it to him when you can trust him with a key to your house.
He gave you the key because he wants you call in to him probably when he is in bed or if he is out that you will be there waiting for you. You could have fun with that; call over when you know he is out and be waiting there in his bedroom for him.
If your ex boyfriend is in your house without your permission, you need to immediately get help. Call the police, or if he has the key to your house, get the lock changed.
Tell him I'd like to go to your house.
It means you had better change the locks as fast as you can.
Change your locks
... Give yourself a wedgie? ^^; Is there any other way
Yes, but give your partner a key!
The assistant curator will give you a painting with a message saying someone wants to meet you at the museum. Its the curator gives you the key to the house in the countryside.
Whatever you do do not ask her to pay part of the rent, that will give her rites.
to give pimps a place to live when their house bunnys are out
If he lives in a house then go to edit town mode and evict him out of his house and into yours. Or you can wait until you get married and then the game will give you the option to move him in.