I voted for Whoa mate, what a hole you've dug, aint got a clue what you should do?!
Sorry you have dug yourself into a hole.
The right thing to do would be tell the 42yr old to go with the other guy who could sort all her problems out and you date the 19yr old.
Your still only a young man yourself with loads of living to be done, really can't see you getting to do it with a 42 year old with son and daughter.
Easy for me to say this but i know it would be harder for you to do, go for the drink with the 19yr old and see how it goes from there, if you like her then go for it, but let the 42yr old know it over or to go to the other guy.
Hope everything works out for you, keep us updated
