Childe knew you had a lover, that's why he tried to be a nice person when he formed a crush on you. You have no idea how much times he probably sang to himself in the bathroom trying to cope.

He was a nice guy, yeah. But he just wanted to punch your lover for taking him away from you. Hell, did you know how happy he was when you announced that you two broke up?

"Finally!..- gah- I mean, I'm.. so sorry to hear that.."

He almost squealed in happiness but he didn't wanna seem like an evil villain wishing upon your break up. So he decided to act. He finally had a chance.