As a teenager I would have hated it if my sister's boyfriend had been around all the time, even if I liked him, so I can see why your DS might mind, but I also agree his reaction is a bit OTT, unless he knows something about BF that he's not telling. You're right, there does have to be a balance, but tipped in favour of the home life of your nuclear family.
All you can do I suppose is impress on bf that he should not assume he can do things in your home, he needs to ask, and if he oversteps the mark, you send him home straightaway, even if he's apologised.
We had certain times that were clearly designated for family (Saturday night dinner, for example) so friends were expected to head off. Waiting for us in bedrooms wasn't allowed.
I would be very wary of your DD getting into a relationship with bf IF he is the kind to use his difficult history as a trump card to get his way, or makes your DD feel responsible for looking after him or keeping him happy, or is very clingy and pulling her into a more enmeshed and serious relationship than she is ready for. I suppose you have to be quite neutral: not for or against the relationship, but always for your DD.
God, I'm not looking forward to this part of parenting.