That bottom leaf is drooping naturally. Your plant is a Dieffenbachia(Dumb cane) Your plant is reaching for sunlight. It needs more........

Agreed, it's Dieffenbachia, probably the #2 plant, right behind peace lily, that is asked about because of poor health/appearance. The usual cause of decline for any potted plant is rotting/suffocating/constricted roots. Are the bottoms of the stems firm where they emerge from the pot?

Would you be able to add a pic of the whole pot, including the other companion plant, to this discussion? IMVHO, the other plant has a lot more to say than the Dief. If it's only leaning for light, as said, (and stems are firm,) it's probably fine. It does look like it's in very low light, from the lack of pronouncement of its' variegation. Maybe someone bumped into it to cause the lean?

It's normal for Dief to lose its' oldest leaf periodically as it ages.

How long have you had this plant? Did a change in the plants' environment coincide with the change in appearance? Have you changed the pot/soil since you've had this plant? Can you please describe the conditions of the spot where you've decided it should live? Not a quiz with right/wrong answers, just think more info is needed to discuss your plant, and definitely to offer any advice.