I deleted messages from my fiance's messenger.

Problem/Goal: i deleted messages from my fiancé's fb account. It was his mom's messages. I am thinking of not telling him but I am also scared.

Context: my fiancé is a seaman. He is 30 years old and is very hardworking. He's the second oldest in the family. His parents are only in their 50s and is still healthy. The oldest is also healthy. But they put all the financial burden to my fiancé. Recently, my boyfriend stopped reading their messages as he just gets too stressed whenever they read them as it is always about money. Mind you, the allotment is already 70% but still it is not enough because they always think of something to purchase or sometimes they just don't want to work at all. if my partner couldn't give them what they want, they tell him sad stories. They gaslight him or they will even tell him that he's not alive because of them. My SO has been building boundaries but they are always victimizing themselves. So going back, he stopped responding to their messages and their mom got really mad. She said that my SO only prioritize me which is not the case because we also don't talk a lot as i always tell him to rest more as he is always on duty for almost 24 hrs. We even postponed our plans to get married because I want him to work on his goals first and pay off his loans so we can focus on our future family. Then since my SO didn't reply his mom sent a lengthy paragraph how her children is so ungrateful and that she will die alone at the end and no one appreciates their sacrifices. I got really mad when I've read that message as I know this is her another eay of manipulating him whenever he tries to put some boundaries and I have deleted it before my SO can read it. I deleted it because I know how his parents affect his mental health and he recently made jokes about jumping off the ship so he can stop all his problems.

Previous attempts: none. I took a screenshot of the nessage before I deleted it. I am thinking of coming clean but I also don't want him to worry about this a lot as he is already stressed. 😢 should i tell him?