Our best advice is to share your post with your significant other. You did a great job of describing the situation you’re in and how it makes you feel. Share it with him and tell him that you’d like him to consider what you’re going through. Ask him to try to see your point of view.
It’s also common for people to admit to things they did not do when repeatedly questioned about an issue, especially if the questioning is nonstop and becomes annoying. In such situations, people think that if they just give in to the pressure, the issue will go away. As you now know, admitting to something you didn’t do simply adds fuel to the fire — the questions don’t stop, they just keep coming.
Working with a therapist is the best way to breakout of these types of interactions and talk about the real issue — your significant other has trust issues that need to be addressed.
Because the two of you have been together so long, after 4 to 6 weeks of therapy you should have a pretty good idea if things look like they’re heading in the right direction. If you don’t see changes in how he copes with his lack of trust, then you might want to consider your options. There is very little point in staying together unless the two of you are able to reestablish trust.