MY gf lied to me plz help?

I been with my gf 8 months now so one day i ask her why didn't she come on to talk to me, (we live a few miles apart so can't se her all day only a few time) she tells me her uncle is using her labtop in the mornings since he forgotten his, (at this time im on my xbox 360 on windows live and on fb i couuldnt cheak my mail ) so she comments syaign she gonna be a shops and such so i said did u really send me a latetr letting me know your uncle was using the labtop? she says yes evven psoted me "the lettter" so then i get my computer back working i ask her for her email to cheak the message she "sent me" so its nto there. she claims she sent it but deletd it cuz she tohguht i bleieve her so not use for it? so i new she was lllying right off the back, so then i go on her page on this site called tagged she has some girl and this lad as her fav friend, so im like who is he why he on ur fav? she like ohh what lad sorry i ment to delete him , so i said why didnt u do it after u realize he was on ur fav she tell me she forgot and didnt se it >.< then she go i swear on my auntie grave to me (shes suppose to be a christian like me btw) so im like okimam blieve her since she sweared , so then i said since u meant to dleet him (she told he its cuz he sent dirty message) so i ask for the message, she sends it and the date said jan 2010 , but its fab 2011 and she didnt have the account until march 2010 so im like are u ylign to me the date is wrong so it took me hours then she admits she lied about the messages and stuff said she done it out of jelaous and didnt want me to think negitive of her . so i gave her a 2nd chance and im wondering was it the right thign to do and how can i trust her agian ? thanks for reading and repyling