AIO for wanting to confront my best friend for being FWB with her ex while letting another guy shower her with expensive gifts?

Me (22F) and my friend (23F), let’s call her L, have been best friends since fourth grade. We’ve shared everything and have been flatmates for about 2,5 years. About 3 years ago our male classmate (I’ll call him A) who we were both only kinda close in high school started inviting us over and to bars for drinks. I quickly realised the group invites were just a way to get to L, he barely acknowledged the rest of us. A was pretty notorious in high school for pining for a girl that eventually blew him off. He’s still sensitive about it.

About a year and a half ago A went into mandatory year-long military service and L was the person he called and texted the most, recommending him books and stuff like that. I remember her being on call for him for an hour every week. She was dating K for about 3 years, an older guy who i thought was pretty cool but they broke up about 8 months ago due to him being low key a political activist and the stress of him being taken by the government and no concrete future with him got to her.

After A returned the whole situation with L got a lot more close. He invited her for events, drinks, etc. and eventually started showing up at the flat every week, moving his one day off so it’s the same as L’s since they both work weekends. He also started to order takeover every time he came over and buying her her favourite expensive candy every week. I have to stress that A acts like a knight. For example our apartment has a queen sized bed in the bedroom and a pull out couch in the kitchen. Usually I take the bed and she takes the couch and we share the bed of there are guests. A sleeps ON THE FLOOR if he stays over instead of L sharing the bed and him taking the couch as is the case with every other guest we ever had. I’ve often caught them cuddling or holding hands.

I’ve asked her a few times how she feels about A and all she told me was that he’s never asked her for anything. About two weeks ago she had her birthday. A took the cake, bringing flowers and gifting her an expensive leather jacket, as well as multiple big plushies. It was a lot. What makes this worse is that A basically lives at work and is supposedly saving up to move away from his family. This isn't pocket change for him—it feels like he's genuinely taking away from his own future to impress her, and she's letting him.

What broke me was when I was over a week ago she told me that her and K are now friends with benefits. I congratulated her but inside I was screaming at the unfairness.

I don't even like A—he's cold to me and barely talks to anyone but L so this isn't about defending a friend I adore. It's about the pattern I'm watching. I feel like my home has become his cover to orbit her. But this feels like she's using him. She'll say things like "I loved that expensive bar, but I'd never go by myself-maybe with A," which reads to me as "maybe if he pays."

I should add: K is tall and conventionally attractive. A isn't. The contrast is glaring.

It bothers me because I live with her, A is constantly in my space, and I'm watching this slow-motion train wreck happen in my own home. I'm the one who'll have to deal with the emotional fallout if A gets hurt like that girl in high school did.

Am I overreacting to her situation? And if I'm
not, should I say something, or will that just ruin our 10+ year friendship?