I am the more eager to send him, therefore, that you may rejoice at seeing him again, and that I may be less anxious. (Philippians 2:28, ESV)Paul is aware that joy... though it can and should be chosen... can also be affected by the good things in life. Epaphroditus returning home to the Philippian Christians will result in their joy.
I wonder if Paul sat back and imagined this reunion. Did he picture Epaphroditus walking back into town? Did he envision him showing up at a fellowship/worship time? Did he think of the hugs that would be shared?
It is no wonder that he would be less anxious for this loving people.