I'm sorry your dad is being neglectful and uncaring. No matter what's going on in his life (a new wife or girlfriend, deadlines at work, duties at home), he has a parental responsibility to see you regularly so a loving bond can be created and maintained. Unfortunately, some fathers are too self-involved to comprehend the hurt they cause their kids. My dad called me degrading names such as “Buffalo Butt” and “Rhino Rump” when I was a girl, damaging my self-esteem and causing me tremendous embarrassment. Now, as an adult and mother, I see how incredibly immature that was of him and I've let go of the misplaced shame I felt. But it took many years.
Your mother probably has some insight that would be helpful about your father's poor character. Perhaps, she hasn't wanted to disparage him in your eyes, but you need to know the truth. His behavior reflects badly on him, not you, and you need to know his past so you can understand why he's acting this way in the present.
If he doesn't see you in person, he should be staying in contact via phone, e-mail, or Skype. If he's not, you and your mom should set up a regular day and time for him to communicate with you. If he doesn't follow through with that, you have a tough decision to make. Do you want to stay connected with him even though it's sporadic, unpredictable, and only on his terms or do you want to take control, limit contact, or possibly even terminate the relationship? Talking with a counselor at school would be beneficial before making such a big decision.
In the meantime, focus on the positive things in your life. Keep a gratitude journal and write down five things you are thankful for each day (Oprah does this). Open up to your friends and family about your dad and get the love and support you need. Set goals for yourself and work hard to achieve them. Develop a rich spiritual life by meditating and spending time in nature. Be good to yourself by eating nutritious foods and exercising. Don't define yourself by your father's neglectful behavior. You are so much more than that.
I wish you the best. I know how painful it is to be shunned by a dad and have so little control over the situation. I'm glad you're reaching out. Please continue to do so. Many girls and women can relate to what you're feeling and experiencing, and we truly do care.