Forgive or Forget Him?

I have a real life scenario to present you with. This problem requires a solution - naturally. My friend offered her situation and she will remain nameless. Here's her situation: One of my best friends, who finished her sophomore year in college (like me), started dating this guy in the fall. At the end of freshman year, they started hanging out...and making out. Over the summer they were able to hangout too and went on a few dates when school wasn't in session. She told me they were dating. They were not officially boyfriend/girlfriend yet - they wanted to see if they would stay in contact over the summer. So when they got back to school, he hooked up with two different girls and never told her - but the two of them were still dating. She said her friends told her something strange might be going on a month or two after his hookups. So she asked them why and they told her what this guy and one of his two hookup girls were saying to each other over a Facebook chat! They told her they were flirtatiously chatting with each other after he officially asked her out! 


Longer story short - she approached him about it after she found out from her friends. He lied to her...way more than once about it. Then he said he was worth her time and that she shouldn't dump him. He promised he would treat her right and they are still dating. So I guess he's treating her better than that drama. 

So would you forgive him? Or forget him and move on?
Answer with a reason!