Consider the temperament of her lover. If it is a hot-tempered man, be prepared for unexpected reactions (severe abuse, assault, etc.). You can choose a time when the house except the two of you to be someone else from the family (in their presence, perhaps he did not dare to radical action). You can report the break-up does not personally, but in an email. At the very least, it will smooth the heat at least for a while.
If your ex-man, in response to your decision falls into hysterics, crying, begging for that you do not throw, try to defuse some joke, can be a little hurt his feelings, thus it cool his ardor.
In any case, a serious conversation with calm deliberation of all points of the i inevitable, remains the only question is when both of you are ready for this conversation. It also happens that the woman, as she seems to have made a firm decision, but it's worth it to see the tearful expression of the faithful, and her heart is compressed, it becomes sorry for him, and the gap is delayed. This situation will not lead to anything good: the more you tighten with a firm "no" to his novel, the more confusion and irritation in your relationship.
To make a firm irrevocable decision, calmly analyze your relationship. You can even equip a piece of paper and a pen. Record on one side, why do you want to leave, that you get in return for this. On the other side note, what would happen if you stay together, you lose, maintaining these relationships.
And remember that your lover - a grown man, able to understand and accept, and you - a fragile woman who has to take care of yourself and your life that you have the right to live the way you want it for yourself, without the obligation to conform to anyone's was expected.
In the end, you can just try to make sure that he wanted you to quit, "falling in his eyes," for example, began to spend too much of his money, flirt with different men, so that he saw it annoying to use it " habits. " The entire arsenal, of course, much more comical look at American comedies, than it may be in fact, so choosing one or the other way, do not forget about personal safety.