If boyfriend already mentioned that he thinks it's ridiculous he can't sleep in her room - yes, hotel. Unless you want sneaking into bed with her in the middle of the night. If hotel is not an option, guest bedroom.
When my boyfriend and I visited my HF after I had completed my year I shared with my oldest girl and he had the guest room. But we were both fine with not sharing and were aware that my HF would not aprove (two teens, one pre-teens - who all had (multiple) kids before I did

but at least the oldest two were married and in their 20s and there was only a 6 year age difference between the oldest and me).
On the other hand... you might be overthinking it

your very observant kids, depending on their age, might very well be aware what can be accomplished between 7.30 am and 3 pm. The time span between 10 pm and 6 am might not make a difference. And allowing AP's boyfriend to share with her might make your kids more comfortable with their own sexuality (and discussing it with you) in the future. But it really depends on how you want it. If you don't want your kids to see they share... they don't share. If you don't want him moving from the guest room into her room in the middle of the night... he can't sleep in your house (until they promise they won't do it). It really depents on how comfortable you are with the whole situation.