Ilusionarme comes from the verb ilusionar, which means to excite, to fill with hope, or to delude. When used reflexively, as in ilusionarme, it means to get one's hopes up or to delude oneself.
In
"Me Equivoqué" is Yami Safdie admitting she got it wrong about someone she was falling for.
She never really liked him for who he was, she liked his potential, the person she imagined he could become. When things fall apart, she refuses to blame him for it. The mistake was hers: she built up a fantasy in her head, expected too much, and fell for an idea rather than the real person in front of her.
It is a song about taking responsibility for your own disappointment, and being honest that sometimes the problem is not the other person, but how much you hoped they would be.