It seems like there are two points, but the first point’s example is this:

For instance, they take part in extra-curriculum together, do some sports, go to movies, etc. The more time they spend with someone, the more likely they are affected by them.

This example demonstrates how friends would spend time together. But I don’t see the example can prove “The more time they spend with someone, the more likely they are affected by them”. This ending sentence was probably trying to connect with the beginning topic sentence to strengthen the point, but the example confuses what you are trying to prove. Furthermore, it seems that the second point is dependent on the first point, which means you can merge the two paragraphs and make them one point. Because the second example you provided can well prove the point you claimed in the first paragraph – spending more time with friends “lays a solid foundation for friends to alter them in several important ways. ”

I might be wrong though. I think this is a great essay that deserves a full score, but just this point confused me.