Updated question: should I be worried?

My boyfriend and I are long distance and freshman in college. We met the spring of our senior year in high school and got to know each other over the summer. We talked all first semester of college and then began dating over winter break. He goes to a school in Ohio while I’m at a school in Kansas. During the second semester he met a lot of new friends and I’m happy for him because that’s what he really wanted. However, the person he has become closest with is a girl. They talk everyday even when he came and visited me because he had a volleyball tournament at my school. Also, they hang out pretty much every weekend in a group, but this last week has been his finals week and he has hung out with her by himself pretty much everyday until 4 in the morning. I know this information from a friend who goes to the same school as my boyfriend. He has mentioned this girl to me, so he is not hiding her, but has not told me fully about the closeness of their relationship. My friend has confirmed that when they hang out until early in the morning nothing bad is happening, neither would ever cross a line while I am in the picture based on both their personalities.