It may have been too late in an outbreak for an accurate swab test. OR it wasn’t HSV. The appearance of the sores 18 days after the oral sex also seems too long for a true primary with only two little scabs present. When you say she tested negative, was that for HSV 1 and 2? I suppose a lot of manual stimulation could be aggressive enough to cause breaks in the skin from the woman from the 26th?