Hi tz6pho,
I can totally sympathize with your situation. My significant other is not in the US either. You might also want to check out the link below and give your support. Rajiv, the immigration attorney who owns this website, is trying to change the law so that spouses of permanent residents will be allowed to adjust their status without the current 5 year wait.
http://boards.immigrationportal.com/forumdisplay.php?forumid=66
Now, to answer your question:
Unfortunately, even with a re-entry permit, there is still no guarantee that you'll be able to return. However, that does not happen very often, and you should be fine as long as you can show ties to the US. When you're entering the US again, make sure you are carrying documents such as tax retunrs (including those years when you're abroad), letter from your employer explaining your long absence, valid driver's license, property deed, apartment lease, library card, etc...
There is also another problem with your strategy. You will not be eligible to apply for citizenship if you leave the country for that long. There are residency requirements that you need to meet in order to qualify for naturalization. For instance, you need to spend more than 2.5 out of 5 years in the US (if you're applying based on a green card derived from employment). Also, none of your trips outside the country should be longer than 6 months unless you have a very good reason, but I don't think that your being sent overseas for 2-3 years counts. In any case, absences of more than a year definitely break the residency requirements.
It wouldn't work even if you come back to the US for a couple of weeks every 6 months. BCIS will see right through that. You can, however, apply for your naturalization 4 years and 1 day after you return from your assignment abroad, assuming that you meet the other requirements.
Feel free to post if you have any other questions. Good luck