Problem with my mother?

I suspect my mother is cheating on my dad.she goes to London everyother month doin (music) but I believe that only to be partialy true.actually I'm almost definatly sure she is cheating.of course she denies it,but she won't let me touch her computer,phone,anything anymore when she used to let me.I've told her what she's doing is wrong but she ignores me.shes about 50 and shes acting immature for her age.idk what to do.I've done everything I can possibly think of. She has changed and its becomeing ridiculous.how she lies about things she doesn't have to lie about.I mean I sneak onto her computer and read in Google history all the things she looks up.its not right she used to be a very good mother now its fifteenth and its killing me.I used to be very close with my mom and now she's screwing some piece of **** in england.Irk wether to talk to my dad and potentialy screw there marriage up or to live in denial.any help will be appreciated,idk who or where to turn to.