So this isn't gonna sound very helpful since when I first played the game in Japanese I couldn't read it so I kinda just skipped through everything until I got what I wanted, but there's 3 basic endings to gun for, one is basically sticking with the swinging until the end, another is to try and stop the swinging (it doesn't end well for MC), and then finally one where you just completely focus on being romantic with the other guy's wife. There should be indicators when you have to make those choices and iirc the other choices just alter what sex scenes you get.