The reason why you have such a hard time is because you are still stuck in your old world view. You know about LoA, but you haven't embodied it yet and so you are still feeling in your old ways. Don't take your reality so seriously. It's just your old thoughts that you have practiced enough to crystallize them.
You don't have to shift to positive thoughts. In fact, you can't do that immediately. Law of attraction doesn't allow it. Emotions like happiness or love are out of reach for you right now. But do you think you can reach for anger? I guess you are somewhere between depression and jealousy right now, so anger should bring you relief and it shouldn't be too hard to reach for anger. After a day or a few days in anger, you can move up in higher emotional regions.
Another method would be to go off the subject completely and think about something else for a while. Supposedly hard to do for you right now, so I would go for the first method.

This is going to be easier said than done but you need to get into a place where you can focus on the relationship you want with them. Take some time to focus on yourself and your happiness. To manifest anything you have to be at peace with yourself otherwise, you'll manifest situations and circumstances related to the low moods you're feeling. Focusing on what is brings more of what is. Your happiness should be the priority, get into that space and then focus on the relationship you want with them. Then things will start to align and manifest with no trouble.