This sounds a lot like me. I’ve seen mice and roaches in their house, but luckily I think they stayed hidden for the most part. The entire house (even bathroom and kitchen) used to be carpeted. Ugly pink carpet and it was FILTHY. Like old gum and dog shit and everything else was cemented to the floor. Luckily they replaced it, but they still live in filth. I also only ever had one friend over, a few months before I moved out. I was always so embarrassed and I made excuses to my friends when they mentioned having sleepovers at my house. I hope your friend is doing a lot better. Thank you for still going to his house and being a good friend, I’m sure he really appreciated that you didn’t judge him for it.