Checking phones in relationships

In the past I was betrayed in a relationship he cheated on me twice and would hide it through his phone and deny it. Now I feel the need to see everyone’s phones.
can cbt therapy or some type of therapy techniques help with me feeling the need to go through my partners phone? What techniques can I use when I feel the need to go through their phone? Why does it irritate me when I don’t know someone’s passcode, especially the person who I am in a relationship with? I feel like I need to know who they are talking to just so I don’t get caught off guard. Has anyone else experienced this?