Here is the relevant portion of a TN case involving the same issues (McDaniel v. McDaniel, 2008-TN-1222.357):
When the trial court must designate the primary residential parent for a minor child, it is required to make the determination "on the basis of the best interest of the child." T.C.A. § 36-6106(a) (2005 & Supp. 2008). Factors to be considered by the trial court are set out in section 36-6106(a)(1) through (10).(fn2)
Tennessee courts use a "comparative fitness" approach to making the determination of primary residential parent. Bah, 668 S.W.2d at 666. "There are literally thousands of things that must be taken into consideration in the lives of young children, and these factors must be reviewed on a comparative approach." Id. (internal citation omitted). Using this approach, the court analyzes the relevant factors as to both parties to determine which parent is comparatively more fit to be the child's primary residential parent.
Husband insists on appeal that the trial court did not give enough weight to the evidence of Wife's past drug use and her association with other drug users, such as the high school friend she dated during the parties' separation. Husband testified, in general, that Wife continued to suffer from drug addiction; Wife testified to the contrary. The trial court found that Wife was not engaging in substance abuse at the time of trial, and that her past drug addiction problems were not a factor in her ability to care for the parties' child. With little documentary or other evidence with which either party's testimony could be corroborated, the resolution of the factual issue of Wife's drug addiction turned on the trial court's determination of the parties' credibility. In such a situation, the trial court is in a better position to resolve the issue because the trial judge is able to observe the witnesses and their demeanor. Wells, 9 S.W.3d at 783. We afford great deference to the trial court's decision to credit Wife's testimony about her past drug use and her assertion that she was no longer engaging in substance abuse. Richards, 70 S.W.3d at 732.
Husband contends, nevertheless, that the trial court erred in designating Wife as the primary residential parent, so we review the evidence in the record. The evidence indicates that, for most of Meagan's life, Wife has been her primary caretaker. From the testimony of both Husband and Wife, it is clear that, during Husband's residential parenting time with Meagan, she has spent substantial time under the supervision of either Husband's parents or Husband's eighteen-year-old paramour. Moreover, Husband's decision to have his girlfriend live with him during his residential parenting time with Meagan, thereby flouting the prohibition in the court-ordered parenting plan, makes it evident that, to Husband, Meagan's best interest is not his top priority. We agree with the trial court's finding that Meagan's best interests are served by designating Wife as the primary residential parent.
In the alternative, Husband contends that his residential parenting time should not have been reduced. The temporary parenting plan in effect at the time of trial gave Husband residential parenting time every other week from 10:00 a.m. on Friday until 10:00 a.m. on Monday, as well as each week from 10:00 a.m. on Wednesday until 8:30 a.m. on Thursday. In the final divorce decree, the permanent parenting plan gave Husband residential parenting time every other week from 6:00 p.m. on Friday until 6:00 p.m. on Sunday, and every Wednesday from 5:00 p.m. until school begins on Thursday, or until 8:00 a.m. when school is not in session. The evidence showed, however, that Meagan's residential parenting time with Husband was most often spent with Husband's parents or his girlfriend, rather than with her father. While Husband can certainly share his parenting time with third parties such as grandparents, the child's time with her other parent, Wife, should not be diminished in favor of time with such third parties rather than her father. We find no error in the trial court's schedule for Husband's alternate residential parenting time.