The NSPCC guidance is that children of opposite genders do not share a room after the eldest one turns 10.
We had a similar experience as my daughter was sharing a room with an older, unrelated boy. He’s a sweet lad but it put both him and my daughter, both reaching puberty, in an uncomfortable position and she didn’t like going there as a result. They just both needed a little more space. I was advised by the school family support worker, who knew both families, to cease all over night contact until the sleeping arrangements were changed.