I am just hating myself because I lied to my boyfriend about my ex who trusted me a lot. Now my boyfriend left me. What should i do now?

It's your loss, buddy. Lying to your boyfriend about an ex is a mistake - there's a reason why he's your "ex". Why did you bring the past into the present - the fact that you had to go back to him when you have your current boyfriend? If you felt that you still had feelings for you ex, then why bother keeping your current boyfriend when all you did was probably waste his time when he could have been with someone else that treated him truthfully that you did? However, if you think it's possible to save the relationship, you can converse with your boyfriend & attempt to make him understand - the reasons that stem up to your actions & so forth. If it's a dead end & he's stubborn to not want to make it work/understand you - then buddy, there's nothing left to do but move on. It's life, shit happens.