A friend of mine is cheating on his girlfriend thoughts?

A friend of mine has recently cheated on his girlfriend. He flirts with a lot of girls as well when out. On social media he follows half naked girls and hasn’t posted his girlfriend in over a year on social media. But friends take really cute loving pictures of them both together and tag him in them. They are both 20 so pretty young. I don’t get why his still with her if his acting this way to be honest? Will it last? She obviously doesn’t know what his been up to either.
A friend of mine is cheating on his girlfriend thoughts?
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