Hi sweetie, welcome to the forum.
Just to get some perspective: There is always two sides to a coin, maybe now you can only see one side which is your target's bitchy gf but you dont know for sure what he is like in the relationship or why he chooses to stay with her right now.
Having said that, worrying about his situation is something you will have to ignore whilst you are using the technique on him, because it can mess with your mindset.
Just focus on sending him love and visualizing the both of you together, ignore her entirely. Dont overcomplicate things.