Be aware that you manipulate for personal gain. It is convenient for him to live with his family, and from you to the missing attention, or affection. Find the strength to recognize this and to make a final decision. It's not easy, especially if you are very attached to him. Need to get rid of psychological dependence, and to say "no" to their own whims.
Once you have decided, act promptly. Tear the relationship completely, leaving neither myself nor him a chance to resume them. Do not reply to calls and SMS, no matter how hard it was. Do not write themselves, avoid random encounters. Imagine him as the enemy, which you do not want to see and hear.
Seeing the inevitability of the break, men can go to all sorts of tricks. For example, to agree with you, that part will be better for both of you, but to offer a "farewell" night. In any case, don't settle, be firm in your intention. Otherwise it is likely that by morning you'll be together again, and your running in circles will continue.
Remove all items that remind of it. Best of all, if you throw them out, in this case yourself will save you from possible memories. Why do you want this nostalgia?
With things just they can throw away. Much harder to get rid of thoughts about it. They need to be replaced by others — sign up for a program or take a vacation and go to rest. New experiences and fun plus a change of environment will gradually displace from your head all thoughts of him.
If you can not leave, plan your life so that you have no free time. You must always be busy — work, Hobbies, friends, sports etc. You just will not have time to reminisce, besides you will gain new friends. Look at them, maybe among them there is someone who will be a worthy replacement for your old man.
To make it easier to make the decision to break off relations with a married man, you must understand that if he lies to his wife — so can deceive others. Including you.