I think a good guild would make a huge difference. That said, let me sum this up for folks that have never played mmos (eg pretty much the same as me).
SWTOR has story modes that require level grinding, etc, to complete. Currently there are X classes per side... which means there are X stories. Once you finish a story in SWTOR, you are "done" with that character and just grind away until you hit the max level (hold on...).
There is life after the max level, but it is best experienced with a large group of friends or in a guild. Keep in mind, once you hit the max level, the only true new content is better items/weapons/etc, group operations, and the hard mode on flashpoints. There really isn't more of your character's story - its just other things that happen in the SWTOR universe. Eventually, you will play everything the game has to offer. When that time comes, you are just repeating the same thing over and over for item drops and maintaining some sort of online friendship with your guild cohorts.
So, for folks like me (RPG oriented), I expect you will enjoy SWTOR. I also expect you will get sick of it and bored after some time. Currently, I'm at a little bit of a stall. I still have in mind that I want to try out some of the republic characters (I really want to play out things as a trooper), but I'm not super into it and have put like an hour or 2 in over the past week or so. If I keep feeling this way, I'll drop my sub and then just jump back in if I find my interests renewed.
Personally, I think that if you find yourself sick of the game, just drop your sub, wait a bit (checking in on the website from time to time to see about new content/changes), and the re-up when an expansion comes out with new content. Odds are you'll start having fun again at that point. Honestly, I can't see myself playing an MMO ad nauseum. I will require breaks and then hopefully be drawn back into the fun again later.