Welcome back! I am sorry you have not received a warmer welcome, but perhaps we can improve upon that.
First, feel free to /befriend me (Grommet) if you find me online. You may have to remind me who you are!
As to Linkshells ("LS"s): I'm not sure if you're in the market for membership in an already-established LS, but you probably should be; otherwise it's very difficult getting started and just generally. (You certainly can keep your own new LS, perhaps when you want to talk only to your smaller group of friends.)
I'll give you four linkshells to consider that I have pearls in and like very much, but you should also read the stickied thread atop this forum for more to consider.
Axiom is a medium-sized shell of long standing with a mix of new, intermediate and older players. http://www.axiom-online.org/ has more information. I am a sackholder there. And by coincidence, Axiom happens to have several recently-returned, or simply brand new, players, so you would have some folks who have that in common with you.
Musketeers is a larger shell weighted towards the veteran side, but friendly, well-organized and still casual, although they do their share of endgame events along with lower-level things. http://ffxi-musketeers.com/
Triumvirate is a shell that spun off from Axiom about 2.5 years ago. Still has a nice mix of levels, and everyone is friendly. http://www.triumvirate-forum.com/ (See the taru bard on their front page? That's me!)
Moghat is a spinoff of sorts from Triumvirate, smaller but very tight-knit; everyone is super friendly. http://moghat.com/
You can shop around a bit, but generally it's best to have just one main social shell. (Heck, I wish all my friends were in just one shell ...)
Oh! Final thought: Thief is an extremely difficult FIRST job. Once you unlock your subjob at 18, you may wish to level other jobs (WAR, MNK) up to 18 or 37 before advancing further on THF. Again, I am sorry you ran into a jerky PT in the Dunes, although we've all had those on occasion!