How do I break up in a respectful / caring manner?

I agree with you.  Your happiness shouldn't depend on one person.  That is an awful lot of pressure on you if you are the only person responsible for his happiness!  Ultimately, we are all responsible for our own happiness.  Connection is an important basic need, and it is hard to be happy without love and belonging and connection, but still that is an awful lot to put on one person.  I would hope that he would have other friends and family, and that you do too.  One of the problems with you being his only source of happiness is that I bet that limits your opportunity to nurture your other relationships, and you might be isolated.  You wrote that he doesn't trust you at all.  What I am reading there is not that you are not trustworthy, but that he is afraid that you will have connection with other people (even if it is not romantic), even with your family and mutual friends.  In other words, he doesn't want you to be happy if it doesn't involve him at the center of it, right?

I would anticipate that he is not going to let you go easily.  You asked how to break up in a respectful and caring manner.  What would you consider respectful and caring?  How about honesty?  If you do care about him, or you don't want him to hurt himself or be in danger, tell him that.  At the same time, your first responsibility is to your own well-being, and if you don't want to be in a relationship with someone, you don't have to be. 

There is a formula that can be helpful for communicating your needs and preferences when someone else might want you to do something else instead.  Part one: Acknowledge the other person's needs or wants (or your concern for them).  Part two: State your decision.  Example, "I want you to be happy, but I can't be your only source of happiness."  

I doubt that he is going to simply accept that.  Be prepared to need to spell it out more clearly, what that means.  Do you want no contact with him at all?  What are you going to stop doing once you break up with him?  You might need to define things like that.  It is not your job to make him feel better, but he will try to convince you that you have to.  

The bottom line is that if you are not happy in the relationship, you are absolutely allowed to move on with your life.  You are a caring person and concerned about being kind and respectful, and the best way to do that in the long run is to be honest.  Ultimately, you can't make him happy, and the best thing would be for him to start learning for himself how to find his own happiness, right?  Not to live in fear of losing his grip on you, which will not make either of you happy to live that way.