My dad is dying and my mom won’t let me cope

My dad was diagnosed with cancer before Christmas, and he’s been given about 3 more months to live. I know that people normally think that in those last few months, people would live life to the fullest. But my dad is too sick to even stand. My mom wants me to spend time at home with my dad, and have “quality family time” before he passes away, but it’s hard to do that when my dad doesn’t even have the energy to have a conversation half the time. It all gets to be so overwhelming and there are days when I just want to leave the house to spend time with my friends and my boyfriend, and just breath. But my mom won’t let me. I keep telling her I just need a break from it all sometimes, but she just tells me I’m a selfish ungrateful bitch. I don’t know what the right decision is. I am closer with my friends than I am with my family, only because I can never discuss anything with my mom without getting yelled at. I haven’t seen my boyfriend in almost 2 weeks, and he’s the only one in my life who actually feels like family to me. I miss him so much and I just really need him right now. But my mom won’t let me use any of our vehicles, and she won’t let me leave the house unless it’s for school. I don’t know what to do. Please help.

****Edit: I guess I should add that my dad has been very cruel to me all my life, and of course I still love him, but part of me just wants all of the pain and hurt he’s caused me and my family to go away, with him. I don’t want my father to die, but I would be lying if I said I didn’t feel the slightest bit of relief. I want to remember the good moments I had with him. I don’t want to constantly see him suffer every day. I don’t want to remember him this way.