Well if that's your attitude I'm off!!
to get a cup of coffee...
Nah I get what you mean about there being no concrete mythology, but most stories, and certainly the more famous versions over the years usually all see Lancelot and Gwen having a fling much later, but no Merlin hasn't been that faithful from the start (and I've never had a huge problem with that).
Well the thing is Lancelot isn't in the "original" mythology at all. He was added later on.