I think Cabel is HELLA sweet to her & very precious.
BUT LOOK, there are actually ppl in this world who react VERY VERY badly to things that don't go the way they like it. You saw how irritated he looked at the thought of her getting dance requests. He looked ready to kill someone. That amount of anger is not a good sign & Rene had to placate him by saying something he would like to hear.
I am not really a fan of Rene (I like her best friend way more) but I understand the way she thinks. You just don't want to piss off ppl like that. & when she says he'd kill her, she doesn't necessarily mean physically, but he is gonna be SO PISSED based on his actions so far & he'd RAGE from her pov. (I feel he will actually be v sad cos this is a webtoon but idk)
The thing is, I have a friend like this, someone who overreacts to the smallest things & no matter how sweet they can be, you still feel like you are walking on glass. It took me a couple of "arguments" or more like her exploding on my face at the SMALLEST MISTAKES I made before we got to know each other better & understand each other (Most of her explosions were because she thought I liked my other friends more & yes I did because I knew them much longer & I had only just met her, but she didn't take that well at all & I couldn't just say it bluntly or she'd be so upset). Clearly Rene & Cabel need this kind of understanding before anything can happen. I am still curious about Elvin tho.