Bare with me this is a long post! Looking for advice..so my stepson (18yr old) met this girl, he asked if she could come over and stay. I said she could come over but not to stay as we had not met this girl. He himself had only met her a couple of times. So the girl comes over seems nice enough everything is fine. Then next weekend (Friday) they go out in town on a date and come back to our home..I ask if she is staying..so she does..and again he asked on Saturday can she stay I said OK but never assume always ask (reason being is my partner and I both work and sometimes up at 5am) so she stays over Saturday...and doesn't leave until Monday night..my partner and I both tell my step son no more overnights (partner was woke 3 times due to talking very loud and laughing). Step son asks if she can come over but not stay l, this is agreed but when either my partner or I go to bed she must go home. Fast forward to the next weekend I wake up at 7.30am Sunday morning to my partner very angry sitting beside me. Turns out stepson has brought her back to our home and is having sx very loudly at 6am..(13yr old sister in next room) my partner goes to go into living room and his friend is laying on the couch. I check my phone and I have a message at 2.30am (I was alseep) asking if she could stay and that she had a bad night and he didn't want to leave her ect ect..but the thing is this message was very different from they way he usually texts (punctuation was used and even a x at the end) I woke them up at 9.30am and told step son to get her out the house. Once said girl left I asked him why she text me from his phone making out to be him asking if she could stay and trying to make out like something was going on...his reply I don't know... I explained that this was manipulative but he doesn't get it and doesn't see anything wrong. I told him I don't want her back in our home. should also mention when she didn't go home on the previous Sunday he left her in our home whilst he went for a driving lesson* which is also why we put a stop to overnights. Anyway...my partner and I were very angry few choice words were said..this is his first girlfriend (although it's "not his girlfriend yet") she has quit uni, her job a day ago and I said to him she will be expecting him to pay for everything now as he works ect. I also said that she only got out a relationship 4 months ago and since they have gotten to know each other she's already slept with him (she is his first) he also told me she never stays at home always between friends uni accommodation ect so I said she could have slept with a couple of people in between (whilst giving a lecture about protection). Now I've calmed I feel bad but I don't want him getting used and I don't want them doing that in the house.. thank you in advance.