Breaking up is hard to do. There have been songs, epic poems, novels and films penned about the subject for as long as each have been in existence. It is one of those things that everyone goes through in life. It's hard for both the one who is doing the breaking up and the one getting dumped. There's no way to sugar coat it. However, there are ways that you can handle the situation for the greater good in both your lives. Look at this from his perspective. Proceed with caution, but don't neglect standing up for what you really want in a relationship...unfortunately, that just isn't him.
Ask him to set aside the time to talk to you. If you have a regular date night, take him to a quiet restaurant where you can talk in peace. You don't want to set his nerves off before the evening has begun so don't alarm him beforehand. On the other hand, don't treat it like a romantic rendezvous. Keep it casual until you are both face to face.
Level with him up front at the start of the conversation. You don't want to get into a conversation that will lead to him talking about his future with you. Make this as painless as possible for both of you. Explain where you stand. If you are open to trying again in a few months, let him know. If you know in your heart that you are done forever, express this. Get out whatever is on your heart and mind. The thing that must remain consistently clear is the fact that this is a break up.
Explain to him what he means to you. Do this only after you have clearly and completely broken things off. This is where things can get tricky. If he starts to hear tender words from you, it can take him back to greater memories. This can make the process more painful, but it is ultimately important for him to hear. You don't want to leave him thinking that you don't love him if you do. Perhaps there are reasons other than your feelings that keep you two apart. Letting him know that he matters to you and that the relationship was important to you is necessary after a long-term relationship experience.
Tell him what led to this decision. If it's his cheating, express this. Yet, don't let his promises of change persuade you to give him another chance if it's not what you want. This explanation should be heard without interruption. Before you start this part of the talk, explain that it's imperative that he hear you out without excusing, explaining or making promises. Then get it out. If he was abusive, he needs to be very clear about the fact that his actions have caused him to lose you forever.
Ask him about his feelings, thoughts and wishes. See what he wants from you at this point. He may want to be friends. He may beg for another chance. He may need space. You can give him space. You can be friends with him. Respond to his needs with your own. If you don't want him in your life at all, you need to be clear about this in the moment. No matter how hard it is, the truth being told up front will help each of you heal much faster.
Say good-bye. Don't linger after a break up. Don't try to get one last good memory in. After you both have said your peace, say good-bye. Don't look back. You are ending things for a reason. If your paths cross again, that's fantastic, but you need to stay true to your heart in this moment.