Sex is depicted lots of ways in fiction. Some sex is for lust, or to achieve some goal, and some is for love.
When the former is depicted, the participants will typically be relatively clothed. Men will pull down their pants, women will pull up their skirts, and if they can be depicted, breasts will be pulled out of bras or bodices.
When the latter is depicted, everyone will be naked (but covered as much as the medium requires, of course.) This is probably to represent intimacy.
The only example that comes to mind is Shakespeare in Love, but I know there are many more out there. Maybe I need rewatch some rom coms.