The trunk does look like a Guava, and those tiny leaves. But still a bit difficult from just those photos.

If your plant is wilting while the soil is still moist, especially if it perks up late in the day as the dark cycle approaches, there's a very high probability you're over-watering. It looks like it's planted in topsoil, which would add additional support to the idea that ultimately too much water and a lack of oxygen in the root zone is at the heart of the problem.

Good luck with the ID. If you were in a more northerly clime I'd suggest Chinese quince as a possible ID. You might consider adding some zonal info or at least a recognizable city near you to your user info.

Al