Personally I think that adult DSCs can be the most challenging for SMs, and Step Dads too! I think the dynamics are particularly difficult. The adult step child can often see themselves as their natural parents peer, especially as their parents are separated, I think kids find it easier to still accept rules and respect that it is their parents home first and foremost, if both parents are still together. But separated, it’s like they see the home as theirs with their lone parent as mates.
The step parent then has a big adult, not doing the washing, not contributing, eating all the food, ignoring them content in the knowledge that their natural parent feels so happy that they’ve been ‘chosen’ over the other parent, that they will let them get away with a lot more than if they’d not separated. They are not stupid either, they are bound to choose the house with more freedom!
My DSD went back to her Mums, and looking back I’m so glad that happened. At least that way her slack behaviour is being taken seriously, her Mum tells her to wash her clothes and she will. If I told her all hell would break loose! If kids are not becoming independent then it’s not good for them to treat a house like a hotel, they should still be learning.
I guess it’s helpful to tell your DP how you feel, however I’d be surprised if he turned around and just sorted it. Usually there are too many guilty or conflicted emotions. I would just start putting your foot down about stuff around the house. It’s completely okay to have limits on how much his girlfriend can come around, to not do his washing, to stop him just eating all the food and start paying or contributing. He won’t respect you otherwise and it’s one way of making him see that you are not invisible and you are not just a skivvy maid.