1. Witcher 2 - Pool is great for sex.
2. Mass Effect - Age of your lover doesn't matter.
3. Witcher 3 - You can't just have sex "with" the pony but "on" the pony as well.
4. Dragon Age Origins - Have sex before going to war, and everything will be alright.
These are just few, there are many others as well which teach us great many things about sex.
5. Skyrim - you might need to kill your partner to marry again