The answer to this question lies in your other post [url]https://www.loveforum.net/love-advice-forum/94421-boyfriend-disturbing-online-behaviour-cheating.html#post1009599[/url]
He's having online sex with strangers and is all spent by the time he's with you. Either that, or he's conditioned himself to respond to his hand and a streaming video and can no longer get off with a real girl.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.