I'm sorry that your mother is acting self-centered and being insensitive to your feelings. Because she has a new boyfriend in her life, she's laser-focused on that relationship and, sadly, is not doing a proper job of mothering you. I strongly suspect that there are people around you who sympathize with your plight but feel helpless to intervene (they probably don't want to tangle with your mom).
Keep searching for allies. Open up about your hurt and show your vulnerability. If you don't find comfort and support in your sphere, go outside of it to find folks who are caring and compassionate: a teacher, a counselor, a neighbor, a leader at your church, peers. In today's society, many people come from broken homes and know what you're experiencing. As I wrote in my article, one in five women identifies herself as a fatherless daughter so there's a whole sisterhood out there that will welcome you.
One of the loneliest times in my life occurred after my dad died, and my mom got involved with a new man. Even though I was an adult with a family of my own, I was shocked and hurt by how she dumped me for him. She abandoned her role as mother and grandmother and started acting like a giddy school girl who was head-over-heels in love with her first crush. It felt like I had lost both parents.
It was hard for me to accept that she was choosing this guy (who, believe me, wasn't much) over my kids and me. Yet, when I did, I realized that it was nothing new but part of a long-time pattern of immature, self-centered behavior. It had nothing to do with me. I used the words of the spiritual teacher, Bryon Katie, as my mantra to go through this trying time: “When you argue against reality, you will suffer.”
You don't have it easy with a dad in prison and a mother preoccupied with a new dude. However, there are plenty of kindhearted people in the world who'd be open to hearing your pain. Keep reaching out, and you will find them. I wish you well!