I have a small leak in my heater core, but a radiator leak solution has managed to stop it, I think.
Nonetheless, I’ve been breathing sweet antifreeze fumes for the past few months.
How bad is that? Is it worse than the acid I dropped back in high school?
Ethylene glycol fumes are not as bad or you as acid fumes. Prolonged breathing can cause dizzy spells. Here’s the material safety data sheet. It lists all the known health effect. If I were you, I wouldn’t get too worked up over this.