How do you know that the other couples you see are not putting it on a bit in public? I know several couples who have shocked me to the core by their split, when you would NEVER have thought they were having troubles just by observing their behaviour in public.
There's no way that any couple could maintain the 'honeymoon' period experienced during the first part of a relationship indefinately, life sees to that. That doesn't mean you stop loving one another though.
If you feel that you are missing out on anything, then why not talk to your partner about it? Personally, I find comminucation key to a good relationship and to leave him, which would be 'suddenly' from his point of view, is a little unfair?
What is it from 'life' you think you're missing out on? Holidays with your friends? Go on a holiday with your friends. Nights out separately from your partner? So go.
Do you still have barriers up with him that you define yourself as difficult to get close to? Do you know why? Could you talk to him about why this is the case and you can both take steps to rectify this? I too am difficult to get close to, I keep most people at arms length, the only person who knows me inside out and back to front is the man I love, so I do know where you're coming from there.
At the end of the day, hon, the grass may be greener on the other side, but it still needs to be cut.