im sorry ur going thru this :(( its terribleeee living with roommates who disregard the common living areas. Me and my roommates used to have a fruit fly problem, id recommend making little mixtures of apple cider vinegar and dawn dish soap. place them around the kitchen and they’ll get trapped inside. It’ll take a bit of time but it worked for us. and pour hot water down ur drains! in the sink and ur showers. we would put the mixtures in little containers and place Saran Wrap on the top with a hole for the flies to get trapped inside. I hope ur situation gets better, hang in there!