Boyfriend cheating on me- dating relation with other girl

We are going through a very bad time in our relationship and then I find out he was seeing a girl in the time we broke up and didn't talk for 9 weeks, they slept together. So rewind 3 years, he has lied to my face all that time. And every time we would argue, that would always come up and he even swore on his moms life he didn't engaged physically with anybody when we were broke up. Now, I'm left devastated because of all the lies and yes the fact that he did sleep with somebody and then came back me really makes me sick. Our relationship is dying and I don't know if I can ever trust him and forgive and forget.
Please ladies, I need to hear your opinion and maybe situations that happened to you because I really don't know if I can let this man be apart of me anymore.

Sorry dear for peeping in to suggest you something as I am a guy, but all I can suggest you is to cut the relationship with that guy and move on in your life, its better to step out of something knowing that it will ruin your life, than to let your whole life ruined....
There is no place of forgiveness and trust on the part of a guy who lies to you whole time and sleeps around with any other girl, he definitely is playing with your feelings and to add this I would call such f***ing guys as losers who just know one thing to sleep around. I would have added some thing here but that would not be an ideal language to use in the forum and I do not want to degrade the value of forum as well as my own value as a member on this forum by using such abusive language.