When is a coldsore at it's most contageous?

I hav suffered from coldsores my whole life (I get them every 3 or 4 months at a guess) and I hate them. Obviously when I have an obvious coldsore (ie: I can see and feel it) I avoid kissing my partner. However, what about if I kiss him a day or so before I start to see or feel the coldsore coming on? How likely is he to get it? This is relly worrying me, we have been together a few years and so far he has never caught a coldsore from me (he has never suffered from them) even when, on the odd occassion I have kissed him with the remains of a coldsore.

I have looked this up on a number of “medical” sites and they all give contradicting facts. Is there a doctor in the house that can help me?