I just got a gf but...

I (23M) just got a gf (21F). I've been single for close to 4 years and I never thought this day would come because I've been an introvert and didn't hangout around girls. How I got into the relationship is a story for another day. In short, it was poor timing and miscommunication.

But my point here is, my now new gf has a female best friend (let's call her Alex) about same age. I work in the same group as Alex, while my gf works in a different group. A guy (22M whom we are going to call Jack) from my group has been flirting with Alex quite a lot. He is a Malay guy and Alex is a nons.

He claims he loves her, but out of her presence, he says it's only for the short time we will be working together. I recently found out that Alex has developed feelings for him too. But the kicker is, Jack has a Malay gf already. I watched him write a love poem for Alex last night and then jumped on a phone call with his girlfriend telling her how much he loves her.

I'm standing here as a guy with a new gf who's best friend is being played by my male friend. I do not know what to do in this situation. I talked to him about it before and he claimed that he is unaware of her feelings and he hasn't confessed his feelings of her yet. I call bs on that because it is clear as day that they both love each other.

I'm not normally into getting into people's bizness but I do not like the idea of playing with people's feelings. It pains me whenever I see them together because even my gf believes they're in love and none of them is aware Jack has a gf already.

I do not know what to do in this situation if I should tell Alex about it (although we work in the same group, I am not close to her), I tell my gf to warn Alex about Jack or if I should just stay quiet and mind my bizness.