I admire your persistence, Dylan.
Some of these trees are set up for failure. The pot is much too small for the foliage mass, or it's simply too small a tree for someone who might be an inexperienced grower to maintain a proper soil moisture level. Quite frequently the tree grows too well until the foliage density becomes too much for the roots to support. You miss watering once and 20% of the roots die, then you're over the edge, so the whole tree dies.
When you do try again (and I hope you will!) go down to the garden center and get yourself some Procumbens Juniper (Japanese Juniper / Green Mound Garden Juniper) in a 3 or even 5 gallon container, and work with that without repotting for the first year.
Even that won't survive a month in the bathroom, but it will forgive a few days neglect at under or overwatering.
There is an article over at
TreeBay Bonsai Tools & Supplies called "Beware the Mallsai"
80 or 90F isn't excessively hot unless your tree is sitting on concrete or up against a wall. We peaked at about 110 a couple years ago and the junipers just laugh it off.