Two simple things, re-stating what others have said.
1) Ask that the open door policy be suspended once per week, when you guys have your night off together, and whether roomie can do you both a huge favor by splitting or st least keeping a very low profile during that time as well. It's just one night a week, it's NOT too much to ask.
2) Ask that they keep the PDA to a minimum around you, if possible. Just a simple request. Many people in your position would feel similarly, and that's why having multiple poly partners live together is so often a problem. Hopefully having more time with your bf will make it easier.
If you can't ask for these things out loud, write then down.
Me, 30ish bi female, been doing solo poly for roughly 5 years. Gia, Clay, and Pike, my partners. Davis, ex/friend/"it's complicated." Eric, Gia's husband. Bee, Gia and Eric's toddler.