How do you deal with your childs father getting into another relationship?

How do you deal with the father of your child getting into another relationship?? we have been broken up for a couple of years (we tried to get back together this last January, but it just didn’t work) we have done very good CO parenting…but he has been dating a girl for two months and moved in together and I literally just found out and kinda got a little depressed about it…more so because he hid it from me and second because he is kinda throwing it in my face everything he is doing for her (which is everything I wanted from the very beginning of our relationship) so it kinda just sucks and I honestly dont know how to handle things