It is grave matter and should be confessed always and frequently. This helps heal and gives the person hope and guidance.
My point is that I don’t know, nor does the Church say that everyone who has an issue with masturbation is constantly in mortal sin. It is grave matter, however the matter to be mortal could not be met and make it more venial for many people who have an addiction or have emotional difficulties which makes them hard to overcome this. And it is a battle and many people do struggle with it.
It is best to seek advice from priest or spiritual advisor as to what they think your culpability is as they will know you more personally and know your struggles etc.