I may have fallen

I've talked with a canon lawyer priest before on what constitutes sin, particularly mortal sin, and I've debated myself for ages on end about what the different requirements for mortal sin really mean. This is a super messy topic that depends a lot on your own personality, tendencies and weaknesses. To give you a sense of scale, it's equally possible that this is a mortal sin and that it's barely even a venial sin depending on essentially minutia.

There's a lot of factors at play here - did you have time to realize it was a sin as it happened? The whole idea of sin is that its a conscious turning away from what God wants and from his goodness and love.

Example: St. Thomas Aquinas argued that wet dreams are not sins because we can't be judged for what we do in our sleep. (I'd like to point out this is an orgasm outside of the marriage act but isn't a sin. Period. Not even venial.) How subconsciously are we talking here - did your will have opportunity to step in and correct the things that your subconscious did - or was this a conscious sin? Another (extreme) example: Let's say I was sleep deprived for weeks on end through no fault of my own. This is hypothetical. Hypothetical me has no functioning mental capacity and has pretty much no conscious will. How accountable am I for the things that I did in that state - even fapping out of habit - given that I have no control over my will and that my subconscious is taking over? This same subconscious that is easily influenced by the devil and is prone to habits without inhibition. Given that this hypothetical person didn't intend to sin, didn't realize it was a sin, and had no will to consent to the sin, and wasn't even actively turning away from God by this action it could be argued that no sin was committed here.

Basically, I suggest asking yourself these questions:
Did you realize it was a sin - Did you realize grave matter was a possibility? Note difference between knowing and realizing. You can know things without realizing it.

If yes, since your will can only stop things it's aware of: Could your will have realistically stopped you? Note that if you realized a second before ejaculation, even turning away wouldn't have stopped it. Sometimes your will just doesn't have time to act - it takes noticeably longer for you to be aware of your action than it does for you to just act. (Wundt, 1879) But you have to be realistic about this, sometimes it just takes a while for us to realize things and become aware of them and that cannot be held against us. If you don't think your will could have stopped you, then don't hold yourself to the standard of consent of the will. But if you honestly think your will could have and should have stopped you then hold it against yourself. But don't set the standard where it doesn't belong - we don't need inaccurate and unnecessary guilt held against us, that's just unproductive.

What you do with your counter is up to you - I mean it's representative of whatever personal goals you want it to represent. You could reset it simply because you ejaculated accidentally and in the wrong place. I (personally) would only reset it if you're sure the sin was mortal. Confess it to be sure, but make sure the priest is aware of the circumstances and don't treat the sin like its mortal if it wasn't.

 

Hasty addendum: There's a third possibility you may want to consider - and it's that if it wasn't mortal and wasn't a serious sin, this could also be the devil attempting to work against your relationship with your wife. Think about it - if for whatever reason this sin wasn't mortal but you believed it was mortal, would you be so likely to spend that kind of beautiful quality time with your wife?

I'm not saying that this was a hundred percent the devil and you have no accountability, but it's just something to help put things in perspective - given that we tend to diagnose ourselves with the worst possible outcomes. In other words - we're biased against ourselves. It's super important that you pray about this to get a reasonable, honest, and inclusive-of-all-factors view of the situation and of your own accountability. And then that you trust God, trust that you've done the necessary soul-searching and that you don't let this become a source of division between you and your wife.

Prayers,
Tryin'

 

I don't think this was as serious as you described. A mortal sin has to meet three criteria mentioned in the Catechism: 1) grave matter that 2) you know is seriously wrong and that 3) you give your free and full consent of the will. The situation you described seems to fail on #2 and #3 (and maybe even #1).

You wanted to be affectionate with your wife, and it appears that you didn't imagine that would cause you to ejaculate unexpectedly (#2, full knowledge: you didn't know).
You intended to show affection; you didn't intend to stimulate yourself. Good point, Tryin', about whether it was possible to stop (#3, full consent of the will).
Wet dreams are not sinful because they do not involve any decision to sin or any choice on the part of the will. If ejaculation in your case just happened, without any act of the will, it may not even be a sin, and almost certainly wasn't grave matter (#1).

Your confessor can give you more concrete advice.

If you're counting no PM, I don't think you have to reset, since you did neither. If you are counting no O, you could reset because of ejaculation. That's up to you.