Newbie dealing with rot and maybe gnats

[Naia]

Got a pretty Phalaenopsis from Home Depot almost 3 months ago. It came in a solid ceramic pot with a solid plastic insert without drainage. Transplanted the whole thing to an orchid insert with lots of drainage. Just pulled the whole thing out and popped it in the new insert, no soil change. After the blooms fell and the stem dried out, repotted with Better-Grow Phalan mix and moss about 5 weeks ago. Cleared out the plug and found the center stop (crown?) was all black and icky. Did some root trimming of the brown and black rotted ones and let it dry out for a day before finishing the repotting. It was doing really well after repotting, until this week.

About 3 weeks ago, we started having an issue with these little black gnat-like flies. We've cleaned out the sink/drains, deep-cleaned the kitchen, basically addressed any area with possible food decay. My husband is convinced it's my orchid (or less likely the other plant my daughter has but is always dry because she forgets to water it). We quarantined the plants to a bathroom with a closed door and have seen a few bugs, so it's possible it's a plant.

For the past couple days, the bottom leaf of my orchid started turning yellow at the stump. I moved it to make sure it was getting indirect light, but the bathroom is also kind of cold. Today, the leaf completely fell off. I unpotted it to take a look at what's going on and found more black rot. But, on the plus side, I didn't see any of those flying bugs, larvae or eggs. The pictures are what it looks like right now. I'm letting it dry out unpotted. I also added a picture from when the blooms fell to see how it was potted. I added some moss to the top to keep it from floating when soaking.

I'm at a loss of what to do. I don't want to get rid of the plant, but the bugs are making my husband (all of us) crazy. I want to try and save it from the rot. Any tips or advice or insight are greatly appreciated!

If the answer is "it's a goner", I'd be sad but that's fine. And any suggestion on where and what to get new that will prevent these bugs (if the plant/soil is the reason)