Instructions
Start a new game with a male Sim. Alternatively, load a save game with a male Sim already created.
Click the icon representing your male Sim to activate him.
Click the "Relationships" tab. Click any of your Sim's male friends and select "Invite Over." For best results, select a Sim with whom you have already formed a close friendship. Wait for the friend to arrive at your home.
Build your relationship with the male friend. Click him and click "Friendly." Use all of the options in the submenu, such as "Chat" and "Enthuse about [subject]," to boost your friendship with him.
Click the friend and select "Romance" once your relationship bar is high. Use the options within this submenu, such as "Flirt" and "Embrace," until the game says your friend finds you extremely irresistible.
Open the "Romance" menu and select "Propose going steady." When the friend accepts, he becomes your Sim's boyfriend.