I agree with all the previous posts, and was about to post about risk shift, but bookworm got in first. It's really easy to think that because your co-pilot hasn't said anything, he's happy. Be careful that he's not thinking the same thing about you.
Just a couple of things more...
If you're flying with a dodgy AI, bear it in mind, and keep very well away from clouds.
You mention that you considered letting down over the sea, if not for the AI. Under such circumstances, without an IMC, I'd suggest talking to D & D. They'll either by able to make sure you are indeed over the sea, or maybe direct you to somewhere with less cloud. You could certainly do with some help under such circumstances.
You're not reckless, nervous, or somewhere in between, just normal and fairly inexperienced. Most of us probably have similar stories...or will in the future. It doesn't take a lot for flying to go from great fun to extremely scary, and when it does it knocks your confidence a bit. You did fine. But if you'd turned back when you wanted to, rather than when Mark did as well, you'd probably have scared yourself less.
Finally, I fly quite often with a friend, and we split up the workload much as you do. But we have one rule that's a little different - if either one of us isn't happy about something, for any reason or no reason at all, we don't do it....at least, we talk about it first.