How can I manage strong feelings of anger or injustice when I am in the situation. I have to meet twice a week with the person who abuses me mentally for long time.

Although it's difficult to not let them hurt you mentally or affect your emotions in a negative way, try to not let them control your emotions. Repeat positive affirmations to remind yourself of your worth, especially before and after seeing this person. Also, just try making it a routine to repeat positive affirmations to yourself daily. Deep breathing also helps. Perhaps get a stress ball or toy to fidget with, and just keep that in your pocket with you at all times. When you no longer let the abuser manipulate your emotions, they will feel powerless which gives you power over them. Perhaps talk to someone you trust when you feel negative emotions caused by this person, and if you don't have anyone in your personal life, you can always reach out to me, other supporters on 7cups, or call or text any helplines. Also, practicing staying in the present moment can be really helpful when you're not with this person and just focus on yourself. Also, try and do activities you enjoy. It will help boost your mood. I know I said a lot, but I hope something was helpful. :)