How does one get over

How does one get over something that felt so real but wasn't. For a few months I was fine, but all of a sudden that's all i can think of. The feeling that I had when I was with him felt so real and it's been fading now but it's still there and idk what to do. It's like everywhere I go I see his ghost. Every person somehow reminds me of him. I see him in everyone. And when we were "together" it felt so real. The stuff that we said to each other. I just can't get over the fact that he was lying. It didnt seem like he was. But he was, because no one just abandons a person like that. I just want to be over it already. I don't want him to cross my mind anymore. I've been keeping it all to myself which I think is making it worse.