I've changed the heater core about two years ago what a PITA that was thinking i would get better heat.I've changed the T-stat also the blend door works.But now it smells like antifreeze in the interior of the car, i don't see anything leaking but the interior window is getting foggy is this an early sign of the core going bad or for what I'm hoping is a leak on one of the hoses.I just moved from NYC to WIXOM,MI a little on the chilly side :(

it either a leak in the core or the lines, but definately a leak

Yes, leak for sure. Check the lines where the firewall is, coolant could be leaking in - maybe....