Ask yourself, what do you expect from this relationship? You want to be my girlfriend on the side or still dreaming about marriage, wedding and the family? If you are satisfied, continue the relationship and enjoy the moment. But if you want more, should make a serious decision - to withdraw this man from the family or find another.
Have a serious talk with your lover. Ask him about your future, what his relationship with his wife and if he was going to leave the family. If his plan is to care and continuation of your novel, just define the exact date. Do not trust his promises and fine words, let them prove their feelings deeds. Try to look at the situation soberly, not to spend several years in meaningless relationships.
Help the man to decide on the care of the family. If he swears his love, but haven't decided on a big change in your life, show their best side. Give him what he lacks in family life, understanding, peace, care, love, passion. Establish yourself as a good owner - keep the apartment clean and cozy, cook delicious. Show that you can give to the beloved all that he lacks, and make you happy, but only if he leaves his wife.
Don't look at your relationship through rose-colored glasses and do not look for excuses for his inaction. If a man has a wife, children, a well-established relationship, it is unlikely he will agree to leave the cozy nest. But even if that happens and you become husband and wife, will you believe in his faithfulness? The man who had once cheated on, most likely, again will lead the mistress.
Let him go, if relationships are suffering and you don't see a happy ending. Just accept that this is not your man, love yourself, find a free and loving guy who will give you all the time and make you lawful wife.