I really need this answer plz plz help?

My mom told me a big secret last summer about my dad. The one i really thought was my dad isnt some other man that i never knew of. It all started when i was out with one of my mom friends at a womans house, very rich woman. When we arrive there the woman keep telling me i look just like my dad (Gary the other man i never knew about) and my sister a girl that i was close with his daughter. i said nothing because the girl (Tiffney) always told me to tell ppl that im her sis and we looked alike everyone thought so. Anyway when i got home my mom ask me how was everything and i told her alll the crazy things the woman said and then my mom broke it to me... i felt not bad but now i cry alot cuz the other man who thinks im his daughter dont no anything and he supports me while the other one gary lives in new york and rearly calls me at all he makes me feel bad i always have to be the one calling and then he might call me for a short while. things are not good i cry i hate cryin would it be better if things were out in the open. My mother friend knew what was goin on and she is my aunt n the girl is my sis no one else knows none of my sisters nor my dad only gary my true dad know and his family. Sometime i dont no who to tell ppl my dad is im so terrified of living this life. My mom and everyone who knows tells me to keep it a secret. Im 15 it disturbs my studies and also gary tells me he loves me but dont show it i love him too i dont no y its hard to not talk to him for too long he treats me so bad but he dont no it. what should i do plz help...