Welcome to the forum lost. Sorry to hear about your predicament. That couple be any of a dozen message apps. Most message apps allow you to change the background, so your screenshot really isn't telling us much. Sorry I couldn't be of more help.
True but I do know that like wechat and some others they show an image or user pic of both parties chatting on the side of each post, this doesn't. This one only identifies the person he's chatting with at the the top of the conversation(I blocked it with green box).