I would put it more diplomatically. If a person cheats on you constantly, lies, steals from you, takes drugs, these are the main reasons for ending a relationship.

i tried my times to say goodbye to my boyfriend but she always asked me to stay...it´s really hard now for me, we talk very seldom but still he cannot accept my no and say he would love me and such. anyway..it´s not your question. I have no problems to say somebody else that it is over but never because he takes drugs or something like this. here chourette is right, the ones need help. If i really love this person i would always try to help him. but i would never stay with someone i don´t love anymore.

I cannot imagine myself saying those words to the person i love. But if it does happen in a situation like that, the words will be in a different way. Firstly, i would sit with him and talk about the matter. This would require alot of patience, and you need to be ready for whatever the consequences. He may not be telling the truth, and you already know that of course. If he cheats, ask him why does he do that. However, If he refuse to listen to your advise or other person advise for that matter; and if he is still doing the same thing or whatever he's doing is jeopardising the relationship, worst hurting you. Only then,you will decide to end the relationship.

You shouldn't let him/her go so far when he lies or cheats you. I'm very faithful in a relation, but I wouldn't forgive him if he cheats me. Everyone tells lies, they can be forgiven, but when he/she cheats you and you know this, it becomes a naivity to stay together. I think cheating is the most upsetable thing in a relationship, if you love that person there are no reasons here for cheat or lie.

Well, maybe I'm too romantic... I think I would bear and forgive anything from the one I love (in particular, I don't agree with Jura: someone who takes drugs needs your help!). So I'll say it's over only if I feel I don't love him any more.