The Russians have crossed the Donets river at multiple points, and, as of a few days ago, the Severo-Lysychansk area has slowly started becoming untenable for the Ukrainians and there is a risk of Russia encircling the region, these are the best troops the UAF have, including "NATO" troops. So they are currently debating whether to hold or retreat to a more defensible position along Slovyansk. And when it comes to Slovyansk itself, the battle to take the city has begun.
Long story short, with the Russians having destroyed all their production facilities, the UAF are running out of materials, and Western weapons are coming in way too slowly. In the meantime, the Russians are using their 10-15 times artillery advantage to pound the UAF, so the casualty rates are also unsustainable. At least 200-300 UAF are being killed every day along with some 600-800 injured. That's more than a battalion per day. The Russians have found a way to push the UAF back while taking very few casualties themselves.
If the UAF is to win, they need to raise a very large force composed of well-trained soldiers with Western equipment. But the West is sending them peanuts. While the UAF failed to modernise themselves over the last 8 years, the West also only prepared the UAF to fight an insurgency, so no heavy weapons.