These are notoriously hard to grow, without the proper knowledge, potting medium and watering regimen. I killed a similar one, Lithops, in similar fashion as yours. Your potting medium is too organic, does not drain well enough, and you would have been better not to water at all.

Christopher

I've had mine for almost 2 years now and during the warmer season I watered it once a month. And only, until the water saturated the soil and drained through. During the colder season, I didn't water it at all. I was fortunate for it to have flowered for me a beautiful, large, yellow bloom.

Now though, the two main "pac-man-shaped" leaves have closed up. I have no idea if that's a normal process or not. I don't know whether to water it or not.

Being you're in central Florida, your humidity level is a lot higher than where I am in San Diego and that may have something to do with it. I've treated the lithops/mesembs as if they were cactus.

And, just so you know Maddi, mine grows mostly in sand with a little bit of composted soil. The soil in the picture may be too "heavy" meaning that it's not quick-draining enough. With mine, when I water, the water runs right out of the drainage hole. When It's done draining I drench it again...to make sure the soil is saturated. Sometimes water can just collect and run off the side of the pot. Drenching it a 2nd time ensures that the entire soil within the pot is saturated. I repeat the process once a month.

Test your soil out: Fill an empty pot the same size with the same soil. Water it as if the plant were in it. Wait a week. If that soil is still the slightest bit damp, it will harm this species. Buy the best quality cactus & succulent mix you can and add sand, perlite, pumice..whatever they sell by you locally that would make your soil gritty and drain out faster. You need a soil that does not retain moisture.

I'm sure someone on the forum can advise both of us more so, please check back. And, please don't give up on trying again; it's a great plant and you were drawn to it for a reason. - best of luck - Neil

These plants are not very water sensitive in Florida, but are incredibly susceptible to crown-rot, lower stem rot (not root rot but more like the rot yours shows), and sunburn. I grow mine outside until nighttime temps drop below 55 and then indoors on a south facing window. During the summer, as you know living in FL, mine gets that Florida rain 2-4 times a week. The leaves have not split and in fact the plant has some sun damage and is at times almost stone-like in texture, indicating it has been grown rather hard. After a long rain it is softer, but hardens up over the following day. However, sometimes standing water will accumulate in the crevice between leaves; my roommate pulled out the dead flowers from my plant last year (!!!) And combined with some standing water, this caused the new leaves in the central stem of my plant to dry up and die. However, it has sent up a side shoot that is actively growing.

I think the key is the Florida heat and high UV levels, and the fact that my soil is 20%grit, 40%perlite, and 50% coconut coir. I learned that coir is especially important in FL because it keeps a high oxygen to water ratio in the root zone, which prevents waterlogged and anoxic roots. I think this and the heat keep this mesemb slowly growing throughout the summer, which helps prevent rot from over-watering. My Fenestraria grows the same way, but if I put it outside too soon and it rains too frequently, many of its leaves will rot in a similar manner to your split rock, from the lower stem but not the roots. But when temperatures reach 80-90, it starts shooting out tons of new growth, even as old growth rots.

tl;dr - pot up your replacement in a mix of grit, perlite, and coir, and put it outside for some heat during the summer. It may survive the rain, but it may be better to leave it on a screened-in porch if you are concerned about losing a stem to crown rot

Long story short, it has exploded due to either overwatering or water-logged soil. There's no saving this plant now. You can retry and make sure you give it proper soil and terracotta pot will be lovely.
I've had mine (Royal Flush var.) since last summer and when it arrived I potted it in a gritter mix than all my other succulents, I water it every 10-14 days, since then it flowered and then in the winter it started to regenerate new set of leaves. Keep in mind that these plants should only have two sets of leaves at a time (maximum), but from the first pic it doesn't seem like that was a problem for you. Since it started to regenerate, I have not watered mine at all since November (almost half a year now), and it is still consuming the leaves from last year, looking healthy and happy.

March:

Just now (new leaves are finally taller and almost bigger than the old set):

Looks great! Always wanted one of those Aloes, just don't have the space at the moment :(