So Oscar was moody and didn't behave well, or didn't behave the way Reeva liked, on some occasions. He accused her of flirting - and maybe she was or maybe she wasn't. He criticized things about her that she got sad about.
I don't see the real relevance of these messages though, other than to show that they had arguments and issues with each other.
You really can't see the relevance that they confirm previous witness testimony about his controlling nature?