Well, the good news is, you got a dive in, you learned some things, and you got back safely.
Now -- Let's look at the dive.
First off, a very long surface swim (and the prospect of repeating it coming back) seems to me to be inadvisable for a very new diver with high gas consumption. I've done dives where there was a very long surface swim to begin the dive, but I wouldn't have done them if I'd thought I would have to do the surface swim back as well. At that point, you do it as a boat dive
In the back of a new diver's mind should be the thought that things might go sideways, due to any number of bits of inexperience, and the place to be when all you want is OUT of the water is not a half mile offshore.
Second, you learned something about communication with an instabuddy. The next time you hook up with somebody you don't know, you'll know to tell them you are brand new, and are managing very little bottom time at present. Then the experienced diver may be able to reevaluate the proposed dive, and see if it makes SENSE for a new diver. There are a lot of us who don't mind doing a short dive, if that's what a new diver can do, but we will change the proposed profile if we have the right information. (I've seen this done on the fly, too, but it wasn't after a half mile swim!)
Third, you've learned that you need to monitor your gas much more often, and keep in touch with your buddy about what remains. As you learned from Lamont's essay, you should agree on a turn pressure and a minimum reserve before you get in the water. If you let your buddy know when you reach turn pressure, he can make whatever modifications he needs to in his planned course to deal with your gas consumption.
I had this happen to me a couple of months ago. I dove with two people new to me. I thought one (on a very small tank) was likely to limit the dive. But it was the other diver who signalled me WAY earlier than I expected that she had reached turn. Having that information allowed me to bring the team shallow much earlier and avoid anybody reaching a "low on air" situation.
Another thing that I hear in the original post is that you would probably enjoy and benefit from reading some more about decompression. Understanding what "no deco limits" really mean, and what you are likely to be able to do, and how to make the decision about when to stay underwater and when to surface, and when the rare occasions are that you should redescend after surfacing, would give you much better ammunition when your buddy is trying to tell you to do something that seems odd. (BTW, if you did a controlled ascent in your situation, there was no need at all to go back down and do an omitted "safety stop".)
It's not a bad thing to have the experience of swimming around a bit on somebody else's regulator. In fact, being relaxed and comfortable while sharing air is an EXCELLENT skill to practice. I would recommend doing it mostly while you still have air in your own tank, though
As far as the swim back in goes, I suspect your buddy stayed underwater simply because it's so much easier for a diver to swim there. It's not good practice, in my opinion. I would have stayed on the surface with you, because it's too difficult for me to track somebody who's above me, and having agreed to dive with you, I committed to being your teammate for that dive. (I might have sworn under my breath a bit, though.)
Finally, you might find some interesting reading in the New Divers forum about how to work on reducing your gas consumption. Although some improvement will simply come with time and dives, there are definitely technique things (proper weighting, horizontal trim, and minimizing extraneous movement) that will substantially drop your consumption. And, after all, more bottom time is what we're all after, right?
Kudos to you for posting this, and for reading the answers. There's a lot to learn on this board.
