Blunder!

MY second game in today's double-rounder at the Mariánské Lázně 50+ seniors was against a Slovak Fide Master.
The game is too complicated for me to properly annotate it tonight, but here is the critical moment.

White to play and draw in Spanton (1854) - Dusan Mikulas (FM 1969), Round 5

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39.Bc2??
I only saw 39.Qe2 after moving. If Black then swops queens, White is out of any danger. That is why Stockfish10 and Komodo10 slightly prefer 39...Be4, but White is fine after, for example, 40.Bc2 or 40.Bc6.
The game continued:
39...Re7 40.Qf4 Qe1+ 41.Qf1 Rfe8
Black's previously passive rooks have come to life, and White is lost.
42.Ba4?
This makes for a quick finish, but the engines' best line, 42.Qxe1 Rxe1+ 43.Kf2 Rh1 44.Bb3 Rxh2+ 45.Kf1 Rh1+ 46.Kf2 h4 47.gxh4 Rxh4, gives Black a huge advantage.
42...Qe3+ 43.Qf2 Qe4 0-1