I was never in an open marriage but "coming months" sounds like a fast moving schedule. This is a very big step to take and I don't think it should be rushed. It's been one day since you found out. Most likely you are still in shock. In my personal opinion, I think both of you need time to process and think about what your paths are before you start walking it. Professional support is great, if you can get it. Both of you matter. Others here may have some advice. Post as often as you need to. We all know what a shock to the system this type of disclosure is.

Sebastian - Take a moment to think about what you want. You should check out the MOM section. Many start the path of an open r'ship, but it does not work. Based on my reading, MOM r'ships work if it stays monogamous with trust. I also tried to have a MOM r'ship but slowly started to see the disrespect from my GID Ex. The common denominator is the one who wants to explore gets greedy and consumed by their needs. They will slowly push your needs away in the name of "discovering who they are and what they want." 

We have three kids, and I understand it's more complicated when they are younger. Write down the boundaries you need HER to follow to protect your heart and feelings. Write down your non-negotiables. She doesn't get to forsake her vows and you because of her 'newfound' identity (but I'm sure you have seen signs before she's verbally admitted it). I would give you the same advice if you were my friend and told me you want to explore outside your marriage. 
 

Hey, all thanks so much for the replies and support. I will be writing a list of boundaries to go over with my wife tomorrow and hope to be working through that. As for our marriage and how it all looks, I think the consensus is to open our relationship over time. She's agreed to not go looking for women until I have had more time to heal. I want to believe her in this, but it's so hard. My trust in her is very diminished and I'm finding myself becoming increasingly paranoid, which is very unlike me.  

I am realizing she's had three months of figuring this out and planning the future about it where I have not, so she is much farther along in her process which is really painful. I don't see us working out long-term. I don't plan on making it work long-term, but our lives are immensely intertwined and we can't just separate immediately without causing more pain for our children.  We are in agreement that the best thing for now is to keep parenting and maintain a lot of our normalcy until things can more gracefully come apart. 

It all sounds nice when I write it, but god, I am just an absolute wreck.  Outside of this forum does anyone have additional resources? I am starting therapy soon, but I don't know if there is anything else. 

Look, I am absolutely sorry to say this but what's that saying - it isn't paranoia if it's true.

Can you imagine going through puberty without noticing your feelings over certain girls?  I can remember the boys I got interested in and the first one was in primary school.  I can still remember his name, what he looked like, he had dark eyes and looked down his nose at me, but then he kept on looking.

That's why it's such a shock.  It is a piece of information that matters so much, it changes how you view your past as well as the present.  That's a lot of shock to process.  It takes time.

Do you have a friend or family member you can confide in?  That I think helps the most - I had a sense of relief when I first spoke to someone else, because it felt so grounding.  

Hey Sebastian!
You seem like a really kind guy, and I am sorry that you are hurting. Just wanted to say that you could check out the late bloomer lesbians on reddit. Many of the women write about coming out to their husbands and how hard it was for them. I read many posts there to gain some perpective even though I am straight woman who was left by a male who came out after 13 year relationship. But I think this thread helped me because I can relate better to how women express their grief.
Anyway, I wish for you that you will always remember, even on hardest days, that even this will pass. You will not feel this pain forever. It will weaken untill it dissapears.