what prevent NATO to send troops into Ukraine only fears from the Russian nuclear power

Since the attack on the Russian strategic bombers and the nuclear radar system before that, were not serving the Ukrainian military,then why they did it ? And whom were mastermind it ? surely not the Ukrainians ,since Russia wouldn't have intention to use nuclear against Ukrainians, because Ukraine isn't a nuclear power, then whom benefits from these attacks, obviously the USA and Europe ,the NATO , because the only reason that prevent NATO countries until now to send troops into Ukraine was not the UN charter and the international law, but their fears from the Russian nuclear arsenal ,so the west first wanted to paralyze the Russian nuclear arsenal