Maybe this should be posted in the "what are the signs that you missed but see clearly now?".
D-day was August 12, 2013. I discovered the texts. All of this was prior to that. After that, there was more, but I'll stick to pre-DD #1.
1. Changed her FB profile picture in March to just her after a trip with a large group that the OM was a part of. First time in +/-9 years that it wasn't both of us. I know that sounds so "high school" but it did strike me as "off" at the time.
2. The cell phone. All of a sudden using her personal phone again and having to add texts every month because she went over. Eventually went to unlimited texts. THIS SHOULD HAVE MADE ME LOOK AT THE BILL BUT IT DIDN'T, AND I'LL NEVER UNDERSTAND WHY I DIDN'T.
3. The "I'm not happy speech" out of no where. Sure, we had our issues like everyone else, but around a month before this started I would have said we were doing good.
4. Stopped showing interest in the dream house we were renovating and had been working on for 2+ years at that point.
5. Starting to go "commando" but only when he was going around. She was always so reserved, and this was completely out of character.
6. Working late. After midnight two and three times a week. I know what she does at her job, and it does not require this.
7. Not wanting to go to bed (just to sleep) and staying up late. Falling asleep on the couch until late. I now know she was texting him.
8. Lots of trips to the mall, but she never bought anything.
9. Our "bye kiss" in the morning became distant when it used to end up with us screwing and being late for work.
10. Our sex life was all of a sudden "boring" when it never had been before.
11. ILYBNILWY speech.
12. Asked to temporarily separate to see if that helped. I didn't know what the problem was.
13. How easily annoyed she was with me. She would get so mad for no reason.
14. Her anxiousness to go hang out on his houseboat all the time. She would take me with her, but I would catch them off by themselves a lot.
15. A pool party where they would end up at the far end of the pool from everyone else. Plus, they were flirting BIG TIME that day and he "had a hard on" when he got out of the pool.
16. New bikini and no record of buying it on our bank statement. It was also WAY outside of the amount of "coverage area" that she normally wore. It was almost a thong, and I refused to let her wear it out of the house. I now know she took it the next day to model it for him. I was originally bought for him.
17. Related to 16, she all of a sudden was paying for things with cash. She NEVER did this before.
18. The sheer distance between us. It was obvious she was pulling away.
19. MY GUT FEELING THAT THERE WAS ANOTHER MAN.
#2 and #19 are the biggest signs.