Stressed (pls read)

Can’t sleep because I’m too stressed but can’t tell anyone because I don’t want people to judge him. So I’ve known about my boyfriend lying about money for about 2 years with the same situation, and he thinks I still don’t know. It’s him paying a relative for a large purchase and he’s getting ripped off. The other part that gets me is said relative knows that I don’t know and in a text that was sent read “it’s better if we keep it from her” both agreeing on that statement. Now,I know I shouldn’t have gone through his phone but in my defense, there were so many signs of something sketchy I knew something was going on. We’re together almost 5 years and we share our money so I feel as though if I have to be open with my money with him, how can he hide such a large thing from me? If he can hide something this large for this long, what else will he/is he hiding? I’m heartbroken that he can lie to me in general let alone for this long. I love him, we have a house and everything together and I don’t want to ruin things but at the same time I can’t live life in a lie. What do I do? (Sorry this is so long)