I do wonder on whose behalf and in what capacity Boris was acting when he made his latest visit to Ukraine/ zelensky. Obviously not the UK as we have a foreign sec/pm and diplomatic service for that sort of thing. I assume that the US/NATO have enough capable people that they don't need to call Boris, so that begs the question whose interests was Boris representing? His track record suggests he is generally for sale, and generally in need of funds so it may be a case of following the money - particularly as his last visit to zelensky was apparently to persuade him not to enter into negotiations that could possibly stop the war.
It may be that Boris is just really good mates with zelensky or just really loves Ukraine I suppose.