How To Forgive A Man Who Betrayed His Wife?

Men are pigs. I know. I used to be one.  Men do this for excitement, fun and to get their ego stroked.  Women do the same thing but for love and attention. Thus--When a man does it  the woman assumes it's for the same reason she might do it--for love.  Nothing's further from the truth.  If the man thinks he loves this other woman, chances are it's the excitement he's in love with.  Let it run it's course and he'll soon realize what a jerk he was for doing this.  Unless you use sex as a bargaining tool and or a reward system for him, he'll most likely not ever do it again. 
Fact:
Less than 2% of men ever marry their mistress.
 
Try to forgive and forget. It's hard but for your long term marriage sake you need to do this.  Most of all try to start having fun with him again.  If you continually bring it up and keep hitting him with the guilt thing you will lose him and your marriage. 

Its better to give him this chance again because neither you want divorce(Of course, you love him) and nor he wants a split-up.
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Some men/women usually go with other women when they look more fun in them but reverts back when they realise that their new found love isn't ready for sacrifices and loyalty for them. His coming back to you can be because of this reason or there can be many other valid good/ugly reasons. But, this one seems to be the most valid one.
Best wishes and prayers for you.

I agree with Lancer.
 
That a man cheats on his wife does not necessarily mean he is not in love with her anymore. Men just love the excitement in that new adventure and out of selfishness, never remember that they would end up hurting people in the process.
 
I am glad you do not want your marriage to collapse since you have a child. Forgive your husband. I know it would be hard to forget this, so I am not going to ask you to do that.
 
And since he asked for your forgiveness which you granted, try not to bring the matter up again. Live your life, learn to trust him back and with time, you would start to forget that it ever happened.
 
I hope and pray that he has learnt his lesson and remains faithful from now on.