ask yourself why you can't bear to break up.
the memories both of you had together?
do the happy ones weigh more than the unhappy ones?
just look at it this way.
if you're holding on together for the sake of holding on, in
this case i would term in commitment,
but she on her part ain't commiting herself to you.
isn't it unfair for you?
as you already said. if you wanna stay together, you'll keep
suspecting her.
till the day she earns back your trust (which i don't know how
is she going to)
you'll keep suspecting her.
standing on her side, how long do you think she can continue
living in the dark? having you suspecting her all the time?
it is only a matter of time before she gives up too.
just have a good talk with her over this matter.
ask her to choose. either you or the other guy.
i believe no man in this world likes to live wearing a green hat
all the time.
be firm with your decision, and good luck 