I feel absolutely mortified for your Son OP!
You say that he has ‘gone off the rails’ because he has a girlfriend! You seem determined to make this a huge issue, you talk about him being disrespectful and you seem very angry!
I fear you are jumping to all of the wrong conclusions and by behaving in a hostile way you are only making things worse, and it probably explains why he is spending so much time at his Girlfriend’s house…he is probably hiding out from you to avoid having a hard time!
You also seem to have a very negative view of his Girlfriend, suggesting that she and her family are immoral!
In 1996 I dated this boy… his parents were concerned I would distract him from his A levels, at the first dinner I went to at his house his mother said ‘I am not ready to be a grandmother yet!’
I literally could have died of embarrassment!
So anyway in 1998 we both went to Uni together, got degrees, got jobs, started pensions, had some holidays, a decade after our first date we got married, bought a house. We did Post Grad degrees while working and earned promotions, and had more holidays after that!
15 years after we started dating we had our first daughter, three years later our second daughter was born.
We have been together for 28 years, and lived incredibly sensible lives!
Yet at the very beginning of our relationship his parents probably would have said the same mean things that you have!
Perhaps in my case they worried more because my Mum actually threw me out of the house for dating my husband and I lived independently in a hostel in a not very affluent area of Birmingham. They must have thought the worst… but it was absolutely unfounded and after a few years they realised that they had made a mistake!
I think that you are being unfair and unreasonable and that your obviously hostility will only push your son away and make the situation much worse!
My relationship with my Mother was never repaired though… she died four years ago…. don’t make the same mistake as her! Don’t ever do something that is so hurtful that you destroy your relationship forever!
Keep calm and try to get to know the girlfriend… she might actually be lovely! They probably are not having sex, and if they are I am sure they will be sensible!
Respect is not a one way thing!