Maine state tax return question

Dh & I live in NH, but DH works in Maine, so he pays ME state tax (which I think is blatant robbery, but anyway, moving on). We were married last Jan. and he didn't change his tax info at work. To the best of my understanding, if one spouse is paying ME tax, they have to pay for both spouses, regardless if their spouse works/lives in ME or not. So yesterday I was doing our taxes online and I did them as filing jointly and seperately to see which would get us more back. Under filing jointly, it said we owe ME $765. Seperately, it doesn't show us owing ME anything. I just want to make sure if we file sep. it's not illegal or something, I don't know why there would be such a big difference between the two. Obviously if we can avoid paying ME so much $, we will, I just don't want to get busted for tax evation or something. Can anyone shed light on this for me?
Thanks!

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