The 3 month separation was due to both our jobs. He was managing a company and had to stay until Xmas to finish up. I had a job starting October so had to go before him.
This sort of transition separation was normal for us.
I don't think he waited till I left to start the affair. I think it crept up on him when I was gone... his life started getting out of control... We had given up our apartment, he was camping at a friend's place, work was very stressful, it was winter, he was miserable, he was wrapping up things administrationally and startting to say goodbye to people and there not being enough time.. So much pressure. And realised along the way how much he didn't want to leave.
In a way I encouraged him into OWs arms unwittingly because the first two weekends after I left, a group of them incl OW went on two weekends away (to OW's brother's 40th birthday party in the countryside - OW brother is my H's oldest friend) and the 2nd weekend the same group (who I am very close to) went on a nostalgic trip back to the place they all went on summer holidays as children. I thought it would be good for him!
But those trips back to childhood, of which OW was a part, started the affair.
In the month following that, WH's communication with me became very needed and lots of 'I love yous' (to me), then it dropped to very little and very unreliable for the 2nd month (Nov) which a deep fatigue becoming aparent by Dec but back to lots of I love yous.
Before getting on the plane he emailed me how much he couldn't wait to see me and how much he needed to sleep and rest..."I could sleep for a thousand years"...
Arrived, all was good for first 24 hrs. Then he started to look crestfallen and angry. Then Bomb.