I can only tell you what I did from my own experience with my daughter.
She recently started studying a few months ago....I'm DF'd. When I found out, my world was shattered because I knew what that meant. My only beautiful girl and I wouldn't have a relationship, if she decided to go through it.
I went through so many, many, many emotions, betrayal, anger, saddness, hurt, being pissed again....you name, it I felt it. I even told her a few things that were wrong, but she was closed off...however, at the end of the day, I came to my conclusion, I truly have un conditional love for her, and my girl is an adult/young adult, she has her own life, I've already lived mine. if she truly believes this is right for her, if it's filling some kind of need for her, or she really trusts that this is true for her...I decided to let her go in love.
I told her, the bottom line is I love you, very much. You know how I feel about WTS, and you know I studied in depth and you know, NOW I try to investigate and learn as much as I can about various things..... if you have any questions, ask me. I'm not going to bible bang you, unless you bible bang me. If this is truly what you want, then I'm not standing in your way. If you need me, I'm always here.
Happy to say, she still calls me. If she asks me something about world events or anything else....I tell her my view point...and I really don't ask her much about her progress with her studies, I pretty much stay out of it.
I've prepared myself for either outcome. I'll let her go in love and peace if need be.
This doesn't mean I'm a wet blanket, I'm surly not.....but at the end of the day.....this was best for me and I haven't put a wedge between us, I'm always here for her.