Completely Panicked, Feeling Stupid

Hello. 
As you read, please try to keep in mind that my S/O and I had absolutely no prior knowledge concerning fleas and how to deal with them.
My S/O and I moved into our first apartment together on January 5th, 2019. In the months prior to moving, my S/O and I were completely thrilled with the idea of living on our own, and becoming first time pet owners.
However, within a few hours of being in our home (and AFTER we had unpacked all our things), we spotted the first of many fleas. They were all over our kitchen floor, and my socks. I discovered my ankles and feet were covered in bites, as were my S/O’s. 
Immediately, we panicked. We saw the first fleas (maybe 5 of them or less) at around 7 o’clock that evening. That night, we stayed up until 5:30 in the morning, frantically trying to solve this issue. With no knowledge on how to deal with fleas, we sprayed a basic flea spray all over our carpets. We stripped our bed and literally EVERY soft cloth item we could find and did what felt like an endless cycle of throwing our things in the laundry. We scrubbed baking soda and salt into all our carpets, and left that and the spray on overnight. The next afternoon, we vacuumed up everything, but left the spray to dry on our tile floors. We also vacuumed our bed, couches, etc. We pulled out our stove and refrigerator in the kitchen and sprayed behind them, too. The next morning we woke over a dozen (maybe even almost two dozen, the details are fuzzy) dead fleas on our tile floor in the kitchen. The entire rest of our apartment in carpeted. We took this as a great sign.
After only a few days of seeing no fleas and gaining no new bites, we (stupidly) figured we had solved the problem. So, we went and (stupidly) adopted a cat from a local shelter and brought her home. 
Obviously, more chaos ensued. Within minutes of having her home, she was excessively grooming, biting, and licking all over her body. Immediately, we knew we had made a mistake. We obsessively combed her with a flea comb, and plucked three fleas out of her fur. So, we also dunked her in a bath of dish soap. We had no record of her being treated with flea prevention from the shelter (we now know that the shelter was completely unreliable as far as health records are concerned), and we made her an appointment for the vet. 
However, as more and more fleas were discovered, our mutual panic only continued to peak. Again, we stayed up all night, vacuuming, washing, spraying, etc. This time from 6 o’clock the night before until 8 in the morning. 
Out of pure stress and exhaustion and guilt, we made the decision to take our cat back to the shelter. As first time pet owners, we felt tremendously stupid and were incredibly guilty for bringing her into an environment where we only caused her stress and pain. So our cat, which we had for just over a day, went back to a shelter. She’s since been adopted by people who have given her a good home. The guilt over making such a dumb decision in adopting an animal so soon after discovering fleas in our home remains.
The same day that we took our cat back (January 11th), an exterminator hired by our realtor came to spray our apartment. He explained what he was going to do (spray our home), and we left for 2 hours. After the two hours were up, our misery had begun to fade and we were thinking, again, that the problem had been solved. The exterminator told us to not vacuum for, and I quote, “as long as we could,” to let the spray effectively kill the bugs in our apartment.
We found only a few dead fleas, and plenty of other dead bugs, and we took that as a good sign.
Fast forward to present, up until yesterday, we believed we were flea free. We had seen no signs of flea dirt, eggs, etc. We had gotten no new bites. We vacuumed continuously for peace of mind, and sprayed flea spray we bought ourselves every two weeks just to be sure.
So… after over a month of not seeing any signs of fleas, we figured this was our moment. We could finally, FINALLY, have a pet now. Yesterday (February 14th) we adopted a dog from a shelter. All was fine for the first day and night. No excessive biting, scratching, or licking. We took this as a great sign because when we had adopted the cat, she had begun excessively grooming/biting within MINUTES of being in our apartment. 
We were feeling great, until this evening (February 15th). It began again. He started biting and scratching, however, no where near as frequently as the cat did. Still, we checked his fur. And there it was – flea dirt. The guilt returns with a vengeance. I can’t stop thinking “How could we be so stupid? How could we do this again?” This time, we are determined to not freak out as much as we did last time. I keep trying to drill into my mind that fleas aren’t a big deal – but I have extreme anxiety and I am already losing sleep over this. It is currently 3 o’clock in the morning as I write this. I haven’t seen any actual fleas on him, but I’m convinced they’ve returned.
We would have gone out to buy a flea collar and more supplies to treat our home, but we are snowed in and the roads are far too dangerous to drive on. And we felt better knowing that he was treated on February 12th with Frontline Plus for flea prevention. 
Tomorrow we plan on returning to the store to get him a flea collar, a flea comb, sprays, etc. Our dog also has a vet appointment for next weekend, February 22. And we will begin the process of cleaning our apartment all over again.
I feel so stupid for bringing another animal into our apartment to deal with this mess, despite my S/O trying to reassure me that we will handle it. I can’t help thinking that if all the things we’ve done haven’t worked yet, what else is there to be done? My anxiety is through the roof and I am physically sick with it. 
What else can we do? Please help and try to refrain from judgement as best you can, although I completely understand it.