How do you know when to end a relationship? If you are asking the question you probably already know the answer. It doesn't really matter what the reasons are, if you have lost that lovin' feeling it may be time to move on.
Every couple will have a different reason for breaking up. Maybe you just don't communicate effectively. Maybe there are too many things the other one does that bug the crap out of you and you find yourselves fighting all the time. If you can't stand to be in the same room with each other, this may be a sign that the two of you should be over.
Even though I said that it doesn't matter what the reasons are, let me give you some examples of reasons someone would want to know when to end a relationship anyway, ok?
Look out for behavior changes. Does your partner come home and do anything they can to stay away from you or not talk to you? There may be something else wrong and you can try to ask them what the matter is. Be prepared for what you might get as an answer.
If they find excuse after excuse why they can't go here or there with you there could be a problem. Assess the situation and see if you can come up with a reasonable explanation. Maybe they don't feel good or something is wrong at work. Or, maybe they just do not want to be in the relationship any more and don't know how to tell you.
If you try to initiate an intimate situation and they put you off, you may have to start to worry that they have something going on with someone else. All too often when one partner loses interest in being intimate it is because they have found someone new and are getting their needs met somewhere else.
Have you noticed they are trying to hide when they are having conversations on the phone, like talking on the phone in the bathroom. Or, maybe they try to hide what they are doing on the computer. If you notice that they have files on the computer that are suddenly password protected then you can bet they are keeping secrets and going behind your back.
If you do notice any of these behaviors then you should be the one to initiate "the talk" and end the relationship. There is no sense in prolonging the agony and ignoring the situation. The relationship is over and you both have known it for a long time. When you do get down to the nitty gritty and have your talk each of you will probably be so relieved you will wonder why you waited.
Life is too short to spend your time with someone you don't love and who doesn't love you. The best thing you can do at this point is to figure out when to end a relationship and get on with your lives.