I'm going to meet a girl in a relationship many times a week
Why do you want to meet somebody that is already in a relationship?
So she can do my laundry for free
It is not good to interfere in another person's relationship. It could cause a lot of pain to the other person in the relationship and you will not look good.
Nah, it's cool. She knows what's going on. We communicate and she's open to this.
What do you think will happen if her boyfriend finds out? He might be less than kind and it could turn violent for you if he gets angry.