Zelensky is not forced by NATO in the sense of being a hostage. Although he does seem to be in over his head. Hence trying to come to a peace deal last year and then being told by NATO, apparently through Boris Johnson, that it wasn’t going to fly.
Since then, especially since the start of the counteroffensive, there have been several reports in US media explaining that the US military pushed Ukraine into the action knowing that it was under supplied and unlikely to achieve its goals. The US ‘hoped’ Ukrainian grit would see the day. Those soldiers are braver than I am for running headfirst through minefields into Russian artillery and defensive lines that Russia had months to prepare. But it’s a careless and tragic use of Ukrainian lives.
The US knows that it has not – likely cannot – supplied Ukraine with what it needs. Neither can the rest of NATO. If Ukraine is to keep fighting, it must look elsewhere. NATO doesn’t have the industry for it. Other US reports confirm this and hint if not confirm that the US interest is not in helping Ukraine to secure it’s independence but to fuel the US economy while trying to undermine the Russian economy. Ukraine is collateral damage for the US. This is the same US that had Ukraine dismantle it’s military through the 90s by insisting on economic reforms attached as conditions to IMF and World Bank loans.
NATO support is waning. Partly because Ukraine is losing. (Partly because the US plans to start a war with China, which will occupy all its attention. In fact, a new cold war may have started this week, according to China and the US.) Zelensky may be able to regain that support but only if things turn around on the battlefield soonish. Until the steps taken to do so clash with US/NATO goals, Zelensky can do what he likes.
It’s not that Zelensky can’t decide for himself. It’s that if he hadn’t already decided to align with the US, he wouldn’t be where he is. He is where he is because his class interests align with those of the US/Anglo-European bourgeoisie.
With this context and clarification of what I meant about the US running the show, I can now address your question.
Seeking weapons outside the NATO-sphere to better achieve NATO goals does not, to be trite, conflict with NATO goals. The US is not going to be upset if Zelensky can get support from elsewhere to keep fighting US enemy #2 (China being enemy #1).
Zelensky is also one man. Just like with Putin, Biden, or anyone else, individual men can’t make decisions of this nature alone.
Can he just fold? Without the support of whoever supports him, if he decides to fold, alone, he’ll be replaced or assassinated or otherwise incapacitated. Does he have the power to fold if he did just take a stand? I’m unsure what the Ukrainian constitution says or of how it will be effected by martial law.