How would you do this

My boyfriend asked me to in with him in 3 to 4 months after he gets the house fixed up and the bedroom rearranged for us both to fit. I know I have go through my things and get rid of stuff I dont need and doesn't fit. My big problem is telling my parents that I am moving out. My dad is like a huge sick and I know he will be against it. My mother probably will be upset at first then not care. How do I tell them? My best friend suggested to wait until closer to moving just act normal and go through my stuff just like I would if we were having a yard sale then when it gets closer slowly pack.