Opinions wanted, am I right or wrong?

Hi guys, I am in a long term serious relationship and engaged and we own a house. I need as many opinions as I can get so I know to react or to not. My partner thinks it's normal to meet up with friends of the opposite sex ALONE drinking until early hours. He has done it before and taken drugs with one in particular who he went to school with and was in the same class. He never asked me if I didnt mind him going he just went so he never respects me.
Drunk last night he told me hes going her house again soon to get drunk and take drugs... I mean are you kidding me?! He thinks this is normal and I am insecure and stopping him from doing what he wants if I say no but I thought being in relationship meant there were boundaries?

Who is in the right here, what advice can you give me to say to him?