If you want to play the song in the style of Roberta Flack, you will probably need to fingerpick it. You could use a simple arpeggeiation, a pattern like R 32 123 or R 23 132 (R=Root, numbers=strings).
Other than that, the key with a song like that imho is not so much the pattern, but the strumming itself. You'd need to strum this very softly. You could try to strum D _uD _ (full measure, counted 1 _+3 _), that should work with the rhythm. I could imagine some other patterns for this, but that would mean 16th note strumming.