Boyfriend cheated on me but his explanation sounds almost believable?

So me, 17F and my bf 19M have been together for 5 months. We are long distance and I’ve visited one time over these past 5 months. He’s very sweet and totally obsessed with me kind of in a scary and unhealthy way. So I thought he would never cheat right?

So the other day I got a screenshot posted in a tiktok I made of him. The comment said “he was just in my phone talking about he miss me” WITH REAL SCREENSHOTS OF HER CALL LOG WITH HIS NUMBER….

So I check my message requests and she said “You and your man played 😂😂” She was a little hostile which I didn’t understand because if I thought my bf had another girlfriend I would be more concerned than angry. She also told me she knew about me but my/our bf told her he blocked me. Which wasn’t true because we were still very much talking and in a relationship.

Anyways, this all happens while I’m on facetime with him…. he’s telling me he can explain and I’m just so hurt I hang up. I didn’t talk to him for 3 days.

Now, his “explanation” is that this other girl was jealous of our relationship because I was “prettier” than her and that he wanted to end things with her and wanted to tell me about her “bothering” him but he didn’t know how to bring it up to me. He said he was afraid if he told me about this girl i would he done with him. I asked him if he really didn’t like this girl why was he calling her everyday. (He would call her after I fell asleep on the phone). And he said “I had to make it seem believable that I liked her so I could let her down easy”

But why? I asked him why didn’t you just block her? He said because she would make new numbers to text him. But she has blocked him before and he also made new numbers to text her.

I started talking to him again but I just find myself to be very angry and hurt. I don’t know what to believe. He really does seem super sorry and sad. I don’t know if I should forgive him or not. I don’t even know if his explanation is the truth. He’s the first guy to treat me right and the first guy I’ve envisioned a future with. Any advice will help.