Getting over someone is tougher than I thought

I just got out of a 4 year relationship because my partner cheated on me. Not only cheated but refused to admit the truth and apologise. My partner is having a great time which I am aware because of social media. What I cant seem to understand is that if I have done nothing wrong then why am I the one who is going into depression while my partner is enjoying life to the fullest?

After a long relationship it's completely normal for you to feel that way. Take small steps every day, definitely try to stop looking at his social media because checking up on him is only going to make you feel worse, once you stop doing that you will start feeling better little by little