Instructions
Buy or find a condom for your character; these items are obtained by purchasing them at a General Store, looting them from NPC homes, and so forth. Using a condom is only possibly if you have one in your inventory.
Find a romantic partner. To engage in sex, you must either find a partner to marry, or hire someone to do it with you. Impress someone with your romantic expressions until they have a heart above their head. Then offer them a ring, and move into a house with them for marriage. Alternatively, visit a rundown town to find a prostitute.
Engage your partner: spouses may need flirting or presents before they will either ask you or can be asked for sex. Other partners will follow you if you have the money and a thumbs-up sign is displayed.
Click on a bed when your partner is following you; if you have a condom in your inventory, you'll be given a choice of whether or not to have protected sex. To use the condom, select "yes."