I lied to my boyfriend and he broke up with me. I want him back. How can I prove that I won't lie again?

Betraying trust is a quite difficult thing to recover from and it takes a lot of time. Simple saying you won’t lie again probably won’t help much. You have to show it with your actions and give him some space to rebuild his trust. Don’t stick too much onto him but make it clear that you are sorry and that you are trying to fix it. It’s his decision whether it will work again, please realise that. Maybe he decides that he doesn’t want to be with you anymore because of your lie, then you will have to accept that. Don’t force anything

Breaking someone's trust can be really easy to do, but earning that trust back is usually very difficult. If you truly want him back, start by explaining the situation in which you lied. However, this won't be enough to earn back his trust; you need to prove your intentions through your actions rather than your words. Understand that this process will take time and it's not something that will happen overnight. Start by doing small things that show him that you genuinely care about him and are sorry for lying in the past. Over time, build up to bigger things once the initial anger has worn down. Some examples are making sure you do not lie again (even small lies), being open and honest with him whenever something happens, working on communication, etc. Also, go into this understanding that, at the end of the day, it is his choice whether or not he is willing to get back together with you. Do not go into it expecting him to for sure take you back, and please respect his choice no matter what.