It starts out with a guy and his head is surrounded by fire effects which Might be triggering, but it's not graphic and he's fine. At least, assumedly; he was very still and quiet.
I'm not sure it counts if like, you were Paying someone to sleep with you and then you go mess about with other women, but she did have his kid and want to be his 'lady,' so... maybe???
Right in the very second scene, and at some point after the green knight scene. No below-the-belt nudity, but they do show the aftermath at one point. If you see a lady offering Gawain his green belt back I recommend skipping that scene (it was so no-explicit that I thought it was just a panic attack, but it gets Gross). There's also another scene when he gets home