how to win her heart now?

i m engaged to a girl and she had a past n she told me i forget everything abt him before engagement.
That guy left her and she was loving her so much. after 6 months of breakup she came
to my life and we r engaged. i know her since last 2 months and
she is the first gal of my life n i love her so much and i did my best
to impress her and i m still trying my best.
but i read her secret chats with her best frined and she is like i still remember
when my EX kissed me and i feel uncomfortable when my fiancee touches me
i was shocked after all these and told her tht we can breakup if u still like that guy n all
but she dont want to breakup and not me as well coz i love her so much
i think she has taken me for granted as she found me without any efforts
whereas that guy left her so she has more value of that guy.
now she says i love u but give me some time.(i dont trust her coz she has different feeling
in her heart but she shows me something different but i love her)
i m very confused but i dont want to breakup but i want her total attention towards me from now
whats after my all efforts she doesnt forget that guy? that will mess my life.
what should i do? thanks

Don't marry her.