Ehhh, he's most likely not going to kill her. In a fight, sure, but killing an opponent that's down and begging for mercy, I don't think this main character is that kind of main character. There are manhua like that, but I don't think this one is.
There's a greater than even chance that leaving her alive will bite him in the ass.
I also don't think she's going to be a love interest. It would not fit the manhua I think. Also, she's quite a bit older and she does not seem to be the type to ever care about someone else.