In my creative writing class, we were taught to treat dialog as full sentences. I'm not sure how true that exactly is since writers often break the rules, but without the comma, your bit of dialog becomes a run on sentence.
So, to answer your question, leave the comma.
However (and this is just opinion really) reading your quote, I wouldn't necessarily thing the ellipse indicated an interruption. Often, it indicates more of a "trailing-off". Em-dashes (—) are better for abrupt stops.
I'd suggest rewording it to give the reader a better sense of what's happening.
"Amanda, I meant to tell you earlier, but—," he stopped. Voice shaking with sorrow he finished, "I couldn't find the words."
I'd also add why he stopped/trailed off and why his voice is shaking with sorrow between the two sentences. This both lengthens the pause (which is a profound moment, I'm assuming, at least for the speaker), and gives the reader a better indication of just how much the man is feeling.