Should I forgive mi ex wife?

Im Adrian . Im 28 yrs and I was married for almost 7 years, actually we have a little boy that is only 19mo.. and I left her, about 7mo ago.
The situation was, that when we where living in mexico, she cheated on me, but I found out that untill we came to california... she was already pregant , I found letters and MSN conversations on her email, that she sent to her friends... so she did take care of erasing incomming emails.. but never erase outgoing emails, and the only reason why I check her stuff was because she was all the time saying that I keep contact with mi ex's , so she check on my email to find nothing...
So, heres the situation, she cheated on my with her ex boss, and I did ask her back on time, if there was something going on between them.. and she told me that nothing was happend, that everything was fine and that it was part of my imagination.. so I keep it that way.. im not a gealous guy I did trust my wife... but only to find out she was cheating.. i think they had a relation for almost 4 mo. and according to one letter the only reason why she stop the relation, was because she got pregnant ( YES THE BABY IT'S MINE, 1000% SURE ) and tha's the only reason... I really dont miss her, but I miss my baby, even when I get to see him often, and she has been crying, and begging me to forgive her.. I just cant.. I dont trust her anymore and I can say that I hate her...
Guys.. what can you say to me...