My husband and I recently got divorced we have two children together. We still love each other very much and are still sleeping together. Is it a sin to sleep with your ex-husband?
It seems to me you are asking the wrong question. I'm wondering why you aren't marrying the man you claim to love and providing a stable home for your two children in which to grow up.
But you are asking if it is wrong to have sex with a man with whom you have no covenant of commitment. The answer to that is, "Yes, it is a sin." So work out your differences and be reconciled to your husband. "Now to the married I command, yet not I but the Lord: A wife is not to depart from her husband. But even if she does depart, let her remain unmarried or be reconciled to her husband. And a husband is not to divorce his wife" (I Corinthians 7:10-11).