1999 Oldsmobile Cutlass heater

I put a new thermostat in my car and when I start up in the moring it take a long time to heat up. So my huspand put antifreeze in my car last night. When I when to start up my car I notice to my car a long time to heat up. I got home and notice that the antifreeze dry up and my huspand didn't see any on the ground and then notice my car inside want wet and we don't know where the antifreeze is going do we need a heater core.