My bunny's eye is bulging and third eyelid is showing. What's wrong?

I am so sorry to hear that Blanco isn't feeling well! With what you are describing, I would be concerned about a few things with Blanco's eye. When the third eyelid is protruding and if the eye seems to be pushing out of the skull more than on the other side, this can mean that either the eye itself is big (and therefore sticking out more from the skull) or that there is something pushing the eye out (such as a mass behind the eye). Rabbits can get diseases within the eye that make them bigger than normal. They also can get abscesses (mostly related to their teeth), cancers, and other diseases that can grow behind the eye. There is also a cancer in their chest that they can develop, called thymoma, that also can result in the eyes being pushed further out than normal, but that usually affects both eyes, and not just one.
I would recommend getting Blanco seen by a veterinarian as soon as possible. The reason for this is that I don't want his eye to dry out, as sometimes it can be hard for them to blink when their eye is protruding more than normal. You can purchase an over-the-counter tear gel to help with this until you can get to the vet. A couple of brands that I recommend are Optixcare and GenTeal. Please ensure that it is the gel only, with no additives for allergy relief or anything else as these can be irritating to rabbits' eyes.
When at the veterinarian, they will evaluate the eye to ensure that it hasn't gotten too dry. They will assess it to see if there are excessively high pressures, and check to see if it is indeed too large. If they suspect that it may be something behind the eye, they may recommend diagnostics, such as imaging to look at the area and blood work to evaluate for systemic health and infections.
I hope this gives you a place to start, and I hope Blanco feels better soon!