My fiancé joined Onlyfans days before me giving birth to our son

I came across this on his debit transactions because he signed into his account on my phone. On January 28th he paid someone $16.05 to someone! He denied it until I showed him his transaction history and then claimed he didn’t know what it was. He will not tell me what he paid a girl for, and I KNOW OnlyFans is free to create an account. I wasted 8 years of my life for this kind of behavior from my ex-husband! My trust has now been broken, once again. I don’t understand why he did this...? I am VERY upset!!! I have cried my eyes out and the thought that he even did this. If I were to create a page and I post nudes/videos, he’d be upset that other men were paying for them! I don’t know what to do and I don’t know if this kind of behavior was okay in previous relationships or not but this crossed boundaries, IS NOT OKAY WITH ME!!! I don’t care about porn, but actually paying someone, when I’m your fiancé and can get whatever for free... HURTS!!!