1. Someone’s cheating
If either you or your partner cheated, then that’s a clear sign that it’s game over for your relationship. Although some people can get over the cheating, for most it is impossible to get past. Cheating creates irreversible damage to the relationship, from which there is no going back. If you have cheated then it is obvious that you do not value your relationship or your partner. If your partner cheats on you once, there is a chance that they will do so again. It all depends on a matter of trust. If you cannot forgive them or trust them again it is best to walk away.
It is okay to admit that your relationship may no longer be working out. Things change and people grow apart. The most important thing is to do what makes you happy and sometimes, walking away can be the best choice to make.