Is my (F20) exclusive talking stage (M20) still in love with another girl

I've been speaking to and going on dates with this guy for just over a month. We've been friends for years and he's admitted that he always kinda had a thing for me. I recently decided that I wanted to pursue him so we started talking and seeing each other. He's a really sweet guy and we have everything in common, he's super lovely to me, he's very affectionate and he seems to really enjoy seeing me.

This past week I went to visit him at his college for a few days. It was so much fun and I got to meet loads of his friends who were all great. We ended up back at one of his friends houses where there was a chart of all their friends and their behaviour (times they've been sick at the club, failed situationship, bodycounts, etc). I was speaking to some of his friends whilst he and some others were looking at the chart. I noticed that he got quite reserved and looked a little sad so I checked on him and he said he was just drunk. We then decided to leave to go home and on the walk back, he started talking to me about why he was upset. On this board was his old situationship's name and the number of people she'd slept with.

Apparently she'd done kind of a number on him and he was basically in love with her but she had been sleeping with other people at the same time as him (which he already knew, but didn't know at the time). I just got a bit worried that maybe he wasn't over her and that I'm just a rebound. I've had situations like this happen before where guys have been super into me and seemed to love me but dropped me as soon as a par girlfriend (who they complained about and said we evil) became available.

IDK, I'm just really into this guy and his reaction to what he saw kinda shocked me and I’m scared of being hurt again.