Have you tried hacking your partner’s social media account? I felt like he’s hiding something - so I did once last year.

Never. I also don't have any interest in checking his personal accounts. So far, there has been no issue at all when it comes to trust. If you feel there's something fishy going on, ask him personally or you can do some other investigation aside from hacking his social media accounts. To me, it's not a mature way of handling the problem.