I made that mistake once, I'm not at all proud of it...still actually quite ashamed - But it did happen, and both he and I took responsibility for it. Did all the right things post mistake. We both came out clean and without an unwanted pregnancy.
Of course, it did cause some ongoing problems...as I don't think either of us fully recovered from it, in the sense of how silly we had been. I think the feelings of guilt really weighed heavily on both sides.
So, I understand how it can happen, it is a mistake for sure...but I've also been there. It was certainly a learning experience for me. Sounds like the OP is already feeling pretty down about it all.
Congrats on getting your lessons learned down. That's a good step