Snapchat and other women

this girl from SOs job added him on snapchat and instead of ignoring it he told her to add me so he could add her after i already told him i didn't want her on his snapchat due to other situations and the fact that he can say shes with his "almost best friend" so it's ok but ive never met either of these people and weve been together for 7 years and hes only known them for a few. Am i in the wrong_