Russia also signed a treaty that said it agreed that Crimea was part of Ukraine, not Russia. It tore that treaty up and invaded Crimea because Ukraine was thinking about not extending Russia's lease on Sevastopol.
No, he didn't.
And even if he did promise the USSR that, I don't see a signed international agreement. Any such personal assurance with no formal agreement could not reasonably be viewed by anyone as anything more than a statement of policy of the then-current administration, not an open-ended binding commitment. I do see a signed treaty, signed much later, committing Russia to respect the sovereignty and territorial integrity of Ukraine, that was in force when it invaded and occupied much of Ukraine.
Russia may not like it (and I'd imagine I wouldn't were I in the same position) but invading countries because of their own sovereign decisions is unlikely to be successful in the long-term.
https://en.topwar.ru/44990-zachem-vms-ssha-sobiralis-remonti...
The link to the official government page is dead now. But I have seen the original with my own eyes back a few years ago. And even saved it as a PDF, but can’t find it now.