Wife and I separated after 12 years of marriage

Unfortunately this is brand new to me and I wish it wasn't happening but what do you do? We finally had the "talk" last night but I've been feeling the distance for about a month now. She got a new position at work and is now really friendly with the maintenance man which works in her area A LOT. She doesn't know I know but we have a mutual friend that ended up telling me they are going to lunch everyday together and way to flirty for comfort even for him. (Very mutual friendship between us) Either way we had the talk and we are separated now. It's fresh and feels very shitty. We live in the same house and share 3 kids together so we are friendly no bad blood as she was my best friend before she was my wife. I don't really have questions I just needed to share and get some advice on whatever you feel I need to know or how to deal with it calmly at all times. Scared mad sad hate being alone but at least I have my kids so that helps big time.