Falling for another guy while being in a relationship

Hi, I'm (18F) in a relationship with my bf (17M) since 1.5 year now. It's really a healthy relationship, he's the sweetest and everything, I'm so glad to have him in my life now, and our relationship is truly fulfilling to me. Like, really, he's not controlling or anything, he's the kindest person I know.

But, since a while, I started to have feelings for another guy (17M) from our friend group.

He's kind, we have a lot of things in commons, etc.

And I thought about it and I don't think it's "just" a crush. It's serious.

I obviously told my bf because we promised each other to be honest and communicative (and also, well, because it's normal, I don't wanna lie or cheat). He told me that, yes, he loves me, but he doesn't want me to stay with him if it's not what I want. "Take your time to choose your path, I'll support you."

And yes, he's sad, I'm sad too. We cried together over the phone for the first time.

But I feel like if I truly was romantically satisfied and invested in my relationship, I wouldn't have a crush so hard on somebody else. And I constantly think about this quote :

"If you fall in love with two people, always choose the second one. Because if you truly loved the first, you wouldn't have fallen again."

It's been a while that I think someday things like :

- I don't see us living together since we're really different.

- I feel like I "outgrew" the relationship, I evolved, and now, I want something that would suit me better.

- I realised how hard it is to settle with someone for a long time. Like, spending ten years aside to someone is huuuuuge! And am I willing to do that with my current bf? I don't know anymore...

- I feel like now that I have this crush, my feelings for my bf are way less significant. And it feels like it's never going to be the same as before again.

I don't want to leave him... But I don't wanna be stuck, miss the opportunity to meet someone awesome, and remain eternally in the relationship with a "What if?". I don't know what to do...

What do you think?