Inform about the breakup in person. Not report the breakup of a relationship via SMS, email, phone call. So you only show disrespect to her husband. You need to meet and talk eye to eye. Thus, you will help the partner to better survive a breakup, to get answers to his questions. Otherwise, you simply deprive him of the chance to fully understand the situation and to understand what the problem is, why it is necessary to leave.
Do not discuss the upcoming separation with strangers. The conversation should take place in private, not in a public place. For these purposes, does not fit a cafe, a restaurant and other establishments. Before you start a conversation, make an introduction that will prepare former lover to unpleasant news.
Together with her husband discuss the situation. Try to explain to your spouse that you are not satisfied with your life together, and specify the reasons that prompted the decision to breakup. Also decide the issue of division of joint property, and if there are children, guardianship over them.
Get rid of guilt. Former partner can make it hard to get over a breakup, constantly pouring out their grief to you. But you are not required to become his "shoulder" where he can cry at any moment. Give him the opportunity to survive this period or to seek help from friends, therapist.
Don't go back and change the decision. If you doubt his actions, rush back and forth, thereby only exacerbate the situation and make the hurt partner. Try to limit communication with her husband for a certain time (for example, month) to not have the opportunity daily to change my mind.
Respect for the former spouse. After you meet a new friend, avoid contact with him phrases in which unflattering spoke about past partner.