Need advice on what to do with this girl

Hey everyone

Like the title says I could use someone else's opinion on what to do with a girl. We've known each other and been talking for about 3 months and more recently I developed feelings for her. Things were going well, we were getting along and I felt like I really understood her but now she's starting to drive me crazy because another guy is involved.

There's a group of us that are friends and we are all in a group chat where I spend about 2 hours a day, mainly just to talk to her. But now she's talking more and more to this other guy and it's clear she's very attracted to him. Another girl complimented him and she replied saying "he's all mine" and they constantly flirt with one another. Every time I see them talk it feels like I'm being stabbed in the heart and I don't know what to do. We still talk and when we do it makes me happy but when this other guy is around she is focused on him.

Normally I'd just cut contact and never talk to her again but doing that is impossible because it would mean losing all my other friends. I literally feel depressed and have never felt this way before in my life, even when I've liked other women.

Any and all advice would be greatly appreciated. Just typing this out has helped to some small extent.