Richie,
The suicides in these cases are rationalisations by later oral tradition. The older ballads invariably imply she simply DIES OF LOVE which is a commonplace in romantic ballads and not unknown in reality.

There is generally no direct link between the kiss and the death of the surviving lover.

Kissing one's dead lover is also a commonplace and in the vast majority of ballads, even more recent ones, there is no implication of catching anything or having a supernatural death, so unless the ballad actually states this you should accept it simply as a desire of a lover. (Stow Brow, The Bramble Briar). What does occur occasionally in older ballads is the supernatural element of weeping at a lover's grave or just mourning generally which makes the ghost, who's shroud is being soaked, appear and admonish the living lover.

There is a tendency from the 18thc onwards to insert explanations into ballads where none previously existed. Many of those who are aware of the older ballads leaping and lingering accept the leapings as leaving the gaps to the listeners' imaginations. The late 18thc and early 19thc Scottish editors were prone to this and it often occurs in oral tradition. Particularly in America there are 2 processes going on in oral tradition. Where a ballad has passed through the hands of mainly passive singers they tend to get whittled down to the basic story and superfluous stanzas are dropped or shunted together. Where it gets passed through the hands of creative people they tend to want to put their own interpretations in and instead of getting shorter they get longer. Myself I prefer those ballads that have been cut back to the bone. The absolute opposite of Peter Buchan's output.