Could Someone Plz Help Me Out With Some School Stress?

my situation is that i recently started dating a girl i had a crush on for a while, but my best friends sister had recently confessed her love for me.. and i felt bad about leaving her alone. and keep in mind im a nice kid…16 in a month. im a stoner and i look older for my age. enyhow, idk what to tell my best friends sister without hurting her. let me go into detail about my new girlfriend: she’s almost 2 years older than me, and i knew she was kinda slutty before i dated her, but i didint think it was a big deal… you know high school dram. anyhow we texted for hours, and she told me she she liked me, and i did the same, but she told me she slept with 22 people /= im a virgin, so i lied and said 10. ive done everything except sex )= . continuing on; she told me about her abusive ex, turning her into a slut /= and how i treated her better than all her boyfriends ever did. she told me i was perfect, and i told her she was perfect. and it was a little weird and fast, but we were and still are in a deep likeness. i don’t believe in love, but we both said we loved each other anyways. everything was sparkling until today. i had the option of skipping school because i had slight flu, that i got from my girlfriend -.- but i decided to go for her…. i realized she meant a lot to me, because me personally hate school(Ive smoked every day for 11 weeks now, but i get A’s and B’s) and regally didn’t feel good. but when i got their she had McDonald for me (=. everything was fine, we were kissing and i held her in my arms and this crazy chick that liked me, took me out of my girlfriends arms and hugs me really hard, and said i love you out loud. my girlfriend has wanted to fight this girl for a very long time. and that bloke the last straw. my girlfriend is ummm… bipolar, and takes a lot of meds and stuff. but she gets moody and easily angry. she planned on fighting her tonight but couldn’t because of her mom. thank god. but she could still fight her anytime at school when im not around. any way we make out after each class, but all my friends tell me reasons to break us up. and all day i get texts from my best friends sister’s friends because i broke her heart. im ******* stressed at this point. and then everything was ok again. she asked me earlier if i minded if she get a ride from her ex boyfriend, and i did, but i didn’t wanna be a dick and say you cant get a ride from a friend /= and he never met me and said im probably just after sex.she showed him my texts i sent her and he thought i was full of ****, and didn’t trust me. and that made her think i was.. and it ******* killed my soul when she accused of just wanting sex, our first argument was a bummer, i had to convince her i really wanted to be with her, even thought i told her she was beautiful every chance necessary.after the fight she said it happened a lot…..she said she gets weird and she cant help it…i dont know if i can keep up with her…im emotionally exhausted…just bitching really. but at least your still reading, thanks. after all that we just talked for a while and im not Sher but i think we went off on a bad note /=. my heart is constantly pounding hard, im lught headed, and have stomach pains, and sick to my stomach, after dating her, i relized shes into tattoos, and piercings and ****, but i don’t mind. she also has self esteem issues, even though shes perfect. she thinks im perfect. oh, and i forgot to tell you her dad dosent like me because im Hawaiian, and not Italian, that hurt, but he can get over it. i feel somewhat depressed half the time and overwhelmed with happiness plz ask questions for more detail. i