@BobB7 - I must disagree. The 8332 rules do not apply unless the parents lived apart at all times during the last 6 months of the year, whether or not they are or were married. The OP said they separated in December.
When both parents have lived with the child more than half the year then the "Qualifying Child of More Than One Person" rules apply. Only one parent can claim all the benefits - they cannot be split.
<a rel="nofollow" target="_blank" href="
https://www.irs.gov/publications/p17/ch03.html#en_US_2016_publink1000204278">https://www.irs.gov/pub...>
The tie-breaking rules might be the deciding factor.
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**