[He's not angry at her per se, but he's angry at Eridan, and he's concerned for her, which makes him unhappy that she got this involved with someone with Eridan's track record.]

Okay, well, if it helps you decide?

For a long time, I was the one who brought his problems to. He's the most needy and insecure asshole you will ever meet, but I must have started on the hating myself train early or something, because I liked talking to him.

I don't think a night went by when he wasn't crying me a fucking ocean about his moirail, Feferi. He loved her, he'd do anything for her, he belonged with her, everything needed to make my stupid younger self think this was actually romantic. Instead of seeing what I should have seen, a pathetic, desperate piece of shit clinging to her gills on the flimsy pretense of a fake moirallegience just to get into her red quadrant.

And when that didn't work out for him, he killed her. He fucking murdered her without hesitating a second. He killed Kanaya, too, even though she never did anything but try to help him with his stupid problems, and he would've killed me if I had bothered to do anything to seem like a threat. He is a selfish, insecure, parasitic, murderous shitwad who has never had a thought for anyone besides himself a night in his life and who will say anything if he thinks it's what you want to hear.

And that is why I am treating this proposition with the deepest possible skepticism and malaise. Do you understand me?