Ex husband anf his new gf

So my ex husband and i divorced it was final in October 2018 we where together 9 years and married for 1 year. Well heres what bugs me his new Girlfriend is my bff me and his gf have known eachother for about 28 years now... When i found out i was so angry i cried i was just in a wow factor and ever since i found out it buggs me how do i handle this? I do have two girls with him that one calls her auntie the other is only 4 months old i was pregnant with her before we divorced an hand her a day before Halloween.. So now i have to share the kids with her too how u would u handle all this