I did something horrible

Just the other night my bf of 1 yr and 6 months were having really hot sex and he asked for me to say who's daddy and as I was about to yell out his name I yelled my ex's name. Now you may ask why? I don't know why, I'd like to blame it on the fact that both their names start with Jo and my ex was my first everything (bf, kiss, first time, 4yr relationship), but I dont know if that would seem as if I'm just making excuses. I was not thinking about him at all, I have not had any contact with him nor has he crossed my mind. I was honestly just enjoying the moment and my bf can not be compared to my ex in any way he is hust too good which is what makes this hurt so much more, he is so good to me (ps he is also ×10 Bette in bed). I feel horrible, I feel I have ruined something so beautiful and even though he says to have forgiven me I feel as I can't forgive myself and I feel that I truly hurt him.

I'm just here hoping to get some advice.