Not in any particular order or importance. I will add as memory allows:

Loosing my virginity at 15 with a slut at a party in a bedroom with other people watching me. I remember I was very quick and there was a fair bit of giggling and commenting going on.

Seeing the diary (a detailed list) of the sexual partners my highschool crush (first love) had had while we were together. I remember groveling with her about it. She denied completely. We stopped having sex but stayed together a few more months. All I wanted to do was cunnilingus with her every time we were together after that.

The first girlfriend who agreed to have a MMF threesome and the harsh reality of the guy she picked (young and athletic).  Once we were in bed together she mostly ignored me and I just watched.

The first time a woman friend told me she thought I was gay.

The time a hot first date told me she was a lesbian while we were getting hot and heavy in bed after she saw my penis.

The time I got my GF an outcall massage and watched another man massage my woman for an hour.

The first time I went to a nude beach and exposed my little willie to random men and women.

The time my GF went into the bathroom with another guy at a party while I waited outside the locked door for 20 minutes. 

My 5 year marriage to M:

The first time she asked me if I wanted to try on her bra and panties.

The first time I wore a bra and panties in front of her.

The time she told me she was willing to "play" (Be with other men).

The first time she dressed up and posed for me so we could take her "dating" profile pics.

The first time she started telling me what kind of porn she wanted to look at. Young and hung, BWC/ BBC, women and couples.

The times she told me in detail about her previous lovers and the fun we had as she teased me about my "interest".

The first time she knew I was wearing panties when we went out together.

The time she went into her daughters bathroom to get the tiny (toddler size) hair bands because the regular ones were too loose for my penis.

When I told her I wanted to touch some of the men I had watched her have sex with. 

The first time I ever let her see me beat off and cum while looking at dick porn with her.

When my wife told me I should be completely shaved. Always.

The first time she wore an ass plug in public.

The first time I let her put an ass plug in me. 

The time I watched her pull into our driveway (from upstairs) in a guys convertible and could see his hands on her legs.

The first time I knew I was eating another guys cum from her pussy after she came home.

The realization how many times I had previously eaten other mens cum from her pussy without knowing.

The moment she told me she had been sleeping with her last boyfriend on and off since we had started dating. 

The first time she tried to put hair bands around me and they kept falling off when my balls retracted.

The first time I let her use a toy on my ass.

The day I realized why she had shaved her legs and pussy every single morning in the shower. 

The time my wife saw me cum without touching myself while I was eating her pussy.

The first time M showed me her vibrator and fake cock collection and how intimidated I was.

The first time I contacted a man my wife had slept with and offered to come over for fun.. (It worked)

The time I helped a guy stroke off after my wife left for work, the morning after.

The first time a man saw me wearing panties. 

The first time I watched her with a black man.

The first time a man watched me eat his cum out of her pussy as soon as he rolled off her.

The time she told me one of her girlfriends knew we we "playing" with other men.

The first time M told me to use her dong in her ass and she admitted her anal sex history. 

One of our first "play" dates that I watched and listened to her with another guy from the loft overlooking the living room.

The time she sent me pics of her dressed up super sexy for a dinner when she was across the country at a business meeting. 

The first time I watched her give a hand job to a guy in a hotel jacuzzi.

The time her eldest daughter dropped an empty TP roll on the coffee table and sneered at me as she walked away.

When she admitted her preference for young men.

When she slept with 6 different college guys (one at a time) from the local college over the course of a few months. 

The first time she entertained two guys during the same evening.

The first time she saw me touch another guys cock.

The first time she watched me suck another guys cock.

The first time she told me to eat a guys cum off her tits.

The first time I saw her tell a "play" date to beat off for her and how she humiliated him. (She declined having sex with him). 

The first time she teased me while sunbathing at a hotel pool knowing I was watching her flirt from our room window.

How things changed (how she changed) after her daughters had both moved out of state for college. 

The first time I bought airfare for a guy she had met online.

The first time one of her girlfriends saw me in panties. 

The time since...:

The times I have called some of the men M slept with while we together and offered myself. (I've been with about 7 so far)

The first time I went to a man's house fully dressed. ( bra, panties, dress and sandals)

The times I have met men who were traveling in hotels for submissive sex. 

The first time I met a young (20 y/o) black guy and I jerked him and let him cum in my mouth. 

The first time I was afraid with an Alpha male. He was the most forceful so far.

The time I cleaned house for a guy wearing panties and a bra. 

The first time I was with a black man (stroking and blow job)

The first time I let a black guy fuck me.

The first time I took a guy bareback and had his jizz leaking out of me all the way home. 

The first time I was fully dressed for a black man.

The first time I was with two black men at the same time. 

The first time I let a guy take pictures of me dressed and sucking on him. 

The time I begged Miles to cum inside me.