My boyfriend worked for a short time in Bahrain last year and I went to visit him. I was warned by my friends before I left because unmarried couples are not allowed to stay together in Bahrain. I think it is the same in many Islamic countries.
Thankfully, we didn't have any problems at the hotel we stayed in. I guess they are a bit more lenient with foreigners. Everything was great and we were treated with great hospitality.
I don't know if it's the same case for people who rent a place together, but I think most hotels will be understanding about it.