Consider Trump's transactionalism. He doesn't care what someone has done for him in the past; it's all about what that someone can do for him in the future. there doesn't seem to be much Putin can do for Trump in the next year, other than agree immediately to whatever Trump proposes as a settlement. That's unlikely.
Meanwhile, Zelensky has agreed to negotiations, knowing that the Russians - when strong-armed into negotiating - will come in with demands so absurdly maximalist that even Trump will see them as absurd. Zelensky can counter with 'NATO membership or we have no choice but to go nuclear - just look at our history with Russia'. The US can't just tell NATO 'accept this new member'; there has to be unanimous agreement among states already in NATO. Hungary and Slovakia are effectively RF client states, so that unanimity won't happen. The US has been very much in the nuclear antiproliferation camp, no idea if Trump will continue, well, anything - but he probably will.
People forget that Ukraine was where the USSR was developing high tech aerospace, so if Ukraine sees going nuclear as their only choice, I'd expect them to have at least one in 9-12 months. Not ICBMs, but Ukraine already has the ability to deliver 50Kg to anywhere in the Eastern RF, so I'd expect that that changes the RF calculus, not to mention European nations in general. The only way to avoid a nuclear exchange on their doorstep is a rapid conventional victory.