Your mom sounds troubled. I believe she's saying she has never hit you b/c she's in denial over what a bad parent she is and she is not ready to face what she did, so she is wants to just say, I never hit you, ever. i say this b/c my mom abandoned me at birth and she denies it to this day. she is also bi-polar. she doesnt want to own up to anything bad she has ever done.
Parents are not perfect people, no, but it sounds like you should stick closer to your dad at this point since your mom has some issues to work through.
Beyond bi polar disorder, parents make up excuses for why they did or didnt do something and they lie sometimes too. My dad lived w/a woman (who he wasnt marrried to, and she wasnt my mom either.) for 11 years, and when i turned 21 and moved out of the house w/my boyfriend, he was upset at me for "shacking up". Um, what was he doing for 11 years? What kind of example did he think he was setting for me? i mean, this woman lived w/us since i was 4 years old,
I am getting off topic but I am just saying parents make excuses for why they do what they do, they lie sometimes, and in the case of bi polar disorders, theyre definitely not stable. I think you should handle the relationship w/your mom very carefully and see if you can go live w/another family member it at all possible. you need somebody to talk to about all this. See if theres anybody else in your family you can confidentially talk to, or maybe a counselor or teacher at school. you need to get this off your chest, not let it build up and hurt you. you must let out those negative feelings and look for positive role models so you can move towards a brighter future. You can do it, I know you can.