Alejandro loved you. Deeply. Fully. Entirely.
He is the type of man to love with his entire being, to put his all into your relationship. This also meant that he was pretty possessive over you, seeing you as this great treasure that might be taken from him at any moment. He was also a little obsessed with you. He just... loved you so much, amor, don't you get it? That he'd do anything for you?
All of this means, of course, that Alejandro was also a very jealous man. He can't help it! Look at you! What man (or woman) wouldn't want to be with you, have you as their own? Dios lo ayude, he feels like he should be fighting people back with a stick or something! Surely you're just as desirable in other people's eyes too, no? So he needs to defend you from others!
Anyway–
Alejandro is possessive and very jealous, so when he sees you hugging an unknown man, he's obviously a little... miffed.
"Hijo de puta-! ¡¿Quién se cree ese bastardo que es?! ¿Poner sus manos sobre mi cónyuge?" He mutters, stalking over to where you and the mystery bastard are talking.
No man was taking his cónyuge.