Will anybody leave their baby will there dad?

In June we will be going to Mexico, nick(my baby) will be three months. We are going so my parents can meet him, my SO is only going for a week. He told me he wants to take nick to his families house for the weekend which is another state in Mexico (5 hour drive). Just them two, so I won't leave my parents, so I thought okay a weekend that's hard but i could do it. Leave Friday, be back Sunday night. Then he told me instead of coming back to my parents house he was just going to come back to California with him. (Nick and I will stay in Mexico for a month) my heart just dropped, I can't leave my baby for a whole month, idk if it's that I don't trust him or idk but I right away said no I can't do it. A weekend will already be hard enough. I just can't picture leaving the baby alone with him at all.