Hi R.,
You have gotten some *great* advice so far.
Something to keep in mind: all babies and children (and adults, for that matter), wake up or almost wake in the middle of the night as part of normal sleep cycles. The trick is, we learn not to come all the way awake, and just fall back asleep: most of us don't even remember waking up.
Your sweetie has proven he can do it, he just fell into the *habit* of waking all the way up recently, and you are in the position of getting him back where he was.
Yes, he's calling for your comfort at night, because he's learned this from you. You've started giving comfort where before, none was needed and he could self-comfort. The trick is just getting him back into the habit of self-comforting again.
This has depended on personality for us: our first (who's now 3) needed a little more of a tough-love approach (he'd fall into the habit very easily: after any cold or bad dream, teething, etc). We'd literally have to give him a cry-it-out night, or he'd keep doing it (thankfully, it just took one night, usually). Now that he's potty-trained, since 2-1/2) no problems.
Our second (who's now 1-1/2), only wakes 2 nights in a row if we make too much of a big deal out of it.
In all, sounds like you won't have much trouble, because he's already accomplished sleeping through the night.
Good job, mama!
T