My boyfriend and I have been dating for almost five months. I met him last school year, he was my classmate in Science. We sit together. He admitted that he liked me. After 3 months, we started dating. I remembered that before we started dating, this girl asked me if he was cute (my boyfriend) and it was obvious that she liked him, but she didn't admit it. She's dating someone now, my boyfriend's friend. But it still bothers me that she and my boyfriend talk every time. I feel like that girl hates me and she's being plastic to me that she's nice and stuff. Idk I just don't really like her because I feel like she's flirting with my boyfriend. I told my boyfriend that I don't like her. I was honest with him, but even though he knows already that I don't like her, he still talks to her. And like he sent me their messages before, he was showing me how funny she is. And one time we were texting, it was really late, we had a bet that whoever falls asleep first has a consequence. I thought I was the only one he was texting but I found out he was texting her too and they have a bet too. What should I tell my boyfriend? I don't want him to feel like I'm controlling him. I just don't really want them talking because its bugging me and it hurting me too.

The problem is not the girl, it's your boyfriend. He is talking to her. He is dating you so he is the one who should care about your feelings and he obviously doesn't.
If they are just texting as friends, what's the problem?

The problem is not the girl, it's your boyfriend. He is talking to her. He is dating you so he is the one who should care about your feelings and he obviously doesn't.
If they are just texting as friends, what's the problem?

I'm scared that maybe that girl still likes him, and she's trying to prove my boyfriend that she's better.

If your boyfriend is loyal to you, you have nothing to worry about. He is your worry, not her.
You guys have only been dating 5 months, he could decide he wants to date her. But that is still on him not her.