Advice: 2nd Wife Marriage

I have been married for 19 years, and we have been through the worse trials and tribulations in both our lives where we had reached bottom, we fought and stood by each all through this and Alhamdurillah with ALLAH`s mercy we have now become very successful. I have dedicated my whole life towards pleasing my husband. We still love each other very much, however he fell in love with someone else and wants to take on a second wife and does not want to let go of me.
I am so confused because we both have a come along way together. He has asked for my Blessings to go ahead but I cannot imagine a life without him, and I am also not willing to share. I am contemplating as to whether I should ask for one talaaq, but we still need to stay under one roof.
I will be completely separated from him and also intimately.

Please advise and what are the rules pertaining to one talaaq.

Jazakallah