Hi MinkMonk, just wanted to offer my sympathy. I was in nearly the exact same shoes as you (2 dc not 3). i could've written your post myself years ago.
Fell in love with a colleague many years ago. I was married with 2 young dc. He was in a LTR. We became friends and after a few years we confessed how we felt about each other. He felt awful for falling for a married woman and didn't want to be a home wrecker. I wanted my marriage to work (even though i had my doubts about my marriage long before this guy came on the scene). We decided not to do anything about our feelings.
I was broken and empty. Told me dh as we were quite open with each other. he was heartbroken and asked me to find another job. I did. It was awful. I hated my new job and missed OM. But dh and i plodded on and life carried on.
OM ended up marrying his girlfriend, moving out of the area and had a dc together. He never left my mind and i would think about him often.
Fast forward 8 years and I was at a conference in the town he had moved to (unknown to me). I was with my boss and he told me that over dinner the previous night he had got chatting to a guy who apparently knew me (we work / trained in the same industry). Couldn't remember his name etc but said he's point him out at dinner that night. It was him.
Cue much awkwardness and catching up that night. It was obvious we felt the same still.
What i wasn't expecting is for my boss to headhunt him after and offer him a job with our company.
The rest they say is history. Within 3 months we realised we couldn't be apart. Both left our spouses etc.
That was 6/7 years ago now. We are very happily married now. Call it fate if you like. It was an awfully painful long journey to get here though.
OP, be careful and look after yourself.