All you have to do is follow the insructions below and your sim will be married easily:

1. Invite your lover round.
2. Make a meal for the other sim.
3. Let the other sim use your toilet.
4. Do somthing fun with them like dancing or watching TV
5. Let them have a sit down.
6. Let them use a coffe or espresso machine.
7. Have a few hugs and kisses.
8. Make sure propose in a large room.
9. Have fun with the new sim.

Hope you have fun making your sims get married!