I'll wager a guess here, because I don't actually know. However, I suspect that this is a mostly positive aspect with some karmic twists. There was something tragic that struck me about this combination, and indeed, a Google search revealed the phrase "sacrifice for the sake of love". I'm thinking of the ability of love to transcend obstacles. Saint Valentine was executed (martyred) for the sake of love, since he refused to stop marrying couples just so there would be enough single men to support an army. Chiron chose death to escape the trauma of a wound that would not heal. Depending on other aspects in the charts, I believe that this aspect would indicate a willingness of the couple to make hard choices (sacrifices) in order to be together (positive) or choose not to be together because of an unwillingness to do so (negative).
Another possible theme: The Chiron partner might be older or an authority figure, such as a mentor or teacher which the Valentine partner idolizes. Messages and communication, lessons in love... Would you be my Valentine?
Much would depend on the rest of the chart. I doubt this aspect would make or break a relationship by itself. Also, unless there were other larger aspects tied to it, I would keep the orb small and I would look for repeating themes elsewhere in the charts.
Thanks for your reply. I have this aspect with someone and we do have a lot of obstacles to be together, but we love each other. I am the Chiron person and he is the Valentine person. The orb is exact. His venus also conjunct my chiron 2 degree orb and this is in my 8th house and his 12th house so the karmic twist sounds interesting. We also have many other aspects Sun-Moon conjunction and venus-pluto conjunction less than 2 degree orb.