Glad that I can help you! As a quick post, some tips for fun sharing/open marriage paths (there are several optionial variants, depending on your and Mei stats and traits)
After the Halloween party in the beginning of the game, choose "Talk about sharing", later at the xmas party "tell her to come home early" or let her stay and(!) tell Mei to relax (a bit of a personal preference here, both options are valid. The first helps to max out lovepoints later). But DO NOT snoop that event, if you have snoop. For beginners it is better to take the stat boost early in the game!
As mentioned, when you go onto the park/hiking event, win the race, have naughty fun with Mei (gaining her the "budding exhibitionist" trait, important for some later events. Fun fact: Even on full romance this trait can become quite handy). Then talk with Jamal about sharing and have Jamal become more friendly, when that choice arrives.
At Valentine´s day, let her have a date with Jamal also (this event you can snoop it is unproblematic, but as said try first with the stat boost, so no snoop on these paths). When you and Mei are on the roof terrace, Make sure to have enoough stats that you can choose "Mei seems to be thinking", then "Use the "L" word" and "Intense strokes".
At the bunny photo shot, choose "Jamal seems to soften up", "Ask Jamal to hang out", "Ask Mei to strip for Jamal" then "Ask Mei to have some fun".
This should set you solidly on a fun sharing/swinging/open marriage path. You can fuck this up later with some choices

, but generally you are on a good way now. Have fun testing out the following events!