there's a 'scientific' explanation to this:

https://goodmenproject.com/featured-...sm-regret-lal/

tl:dr version, it's inbuilt, happens to everyone, just some people get it alot worse

to really get over the regret, you probably need to think why you regret it:
is it because of the nature/legality of the transaction (if so, go to brothels next time),
price (spend less, punt less frequently),
cheating/unfaithful/moral standards etc (not sure how you can be helped here, seems to be a natural inbuilt thing we have)