I don't like my boyfriends son?

We have been together 3yrs. I have 2 children only one lives at home. My boyfriend moved in my home which I purchased prior to our meeting. He has 2 children who have always lived out of state, each from different mothers.We discussed before moving in together that I had no intention of raising anymore children and he agreed. I have had step children in the past and also helped raise 3 other troubled teens. I never met a child I didn't like until now..My bf has never been more than a summer or holiday father, His children have never lived with him. His son now 15 came to live with us about 3 months ago. His son calls one night saying kids are making fun of him at school and wants to move here. I was having some unrelated family issues. I was not home or made aware of this. To my surprise my bf shows up son in tow. He gives him my oldest sons room that I had turned into a room for my son and granddaughter to use. They use it at least monthly. I asked him again to build a room on. He says he doesn't feel as though he should add a room to a home that isn't his. I understand his point but I feel as if I have been disrespected and taken advantage of. I have never really like his son but was willing to put up with him for 3 to 5 yrs until he moved out, went to college etc. It was worth it to have this wonderful man in my life. Now my son no longer has a place to sleep when he is here. He granddaughters have to share the couch which infuriates me even more. I have become withdrawn, mean and hateful. This is not normal for me. His son has also never been taught any manners or responsibility such as cleaning up after yourself, wear a shirt at the table, limit shower time to ensure there is enough hot water for everyone and other normal household rules others in my home abide by. He is disrespectful and will go into anyone's room lay on their beds even after he has gotten hot and sweaty. I have asked my bf to move out telling him I didn't feel same anymore. I don't have the heart to tell him I don't like his son. Even the teachers at his school have made negative remarks about him .I would never ask him to choose. I believe his son should come first and he definitely needs his father's attention. My problem is my bf won't move out. He says he can tell I still love him and he knows we are meant to be together. I feel the same way or did until his son came here.Yes I had previously agreed to be a summer and holiday step mom but I didn't agree to this. How do I get him out of my home and get on with my life. Please help