It is not a pre requisite that you need to be a Scottish Nationalist to support Scottish Independence.
Indeed there are a fair number of folks who support Independence without being Nationalists.
There are many who regard themselves an Internationalists, as Socialists, as Republicans, and many who do not regard themselves as anything other than ordinary Citizens.
In the YES Scotland Campaign you have them all. There are the Scottish Greens who do not regard themselves as Nationalists, there is the Scottish Socialists,Trade Unionists,Scottish Labour for Independence, There is the Scottish Republican movement, There is is even a Centre- Right wing organisation. And of course many folks not in any organisation whatsoever, and of course there are the Nationalists too.
What do they all have in common? If they are not all Nationalists, what are they? They are all Rationalists!
The can all see that Scottish Independence makes absolute sense, and they have all rationalised it for themselves from their own individual perspectives. It makes absolute and convincing sense!
It conversely makes very little to no sense at all, to remain chained to the British State, It is detrimental and divisive, and serves the smallest minority at the expense and detriment to the majority.
In effect, It is barely functional in a real and rewarding sense to anyone, but those who leech of the back of the people.
I need say not much more than that, except to direct you to an excellent perspective from an avowed Unionist who has begun to rationalise it all for himself. I recommend you read Kevin McKennas Guardian article.