Tax Time: joint vs single

Today, is the first time Matt and I tried to do our taxes together, since we're engaged now. We've always just done it separately even though "technically" we are common-law. Shhh, don't tell anyone.

I always thought that once you file things together, it would be to your advantage? We did the whole thing, as a couple and all was fine, but when we started adding in my info, the dollar amount starting going down and down and down.  We were royally confused. These stupid tax programs make some kind of random calculation and suddenly you go from 1400$ return, to 0$ return. It doesn't tell you why, it just steals from you and you have no idea why. WHY?

I feel the urge to go to an Accountant and get someone to help us, who knows what they are doing! But, Matt (being a man- no offense to you or any other men out there) thinks that he is perfectly capable of doing it, and doesn't want to pay someone money to do it. But, if it means we will get more back, than wouldn't it be worth it?  Do you have any experience working with an Accountant? when is it worth it, and when isn't it?

This is the tax program we've used for the last 3 years. Are some programs better than others? ..........................

So, the final result after doing a joined tax form, and a seperate one, was that it we got more money back by actually filing separately. Since I make so little, and Matt's makes almost 3 times as much as me, (damn!) we thought it would benefit us. It didn't benefit us at all. I was not able to find any good articles, or find any information about taxes and what to do in our situation..... any suggestions? anyone have experience with this?

We decided we will file separately for now, but what happens when we get married? Can we continue to file separately? I'm confused about the whole thing. Accountant-- here I come!!