On the issue of that which must not be discussed I think his tactical eye has become VERY sharp and he had no problem making calm waiting moves when it was the most accurate way to proceed. You had no chance.
Are these the same players??

Indeed.. I know my opening was asking for trouble, but didn't think it would get shattered like that. I saw the Bxf4 tactic a bit too late as well...

I believe 5.Bb5 is what gave you a bad position out of the opening, or a comfortable position to your opponent, however you like to think about it.
8.d3 and 9.e5 also look like small mistakes to me but your problems started after 5.Bb5
***
About the player, upsets like those can happen, I just lost a completely winning position against a 1300 but outplayed a 1600 and won the game due to my better piece activity.

5.Bb5 is my theoretical preparation - but I misplayed the positions afterwards, and black got much better. 5.Bb5 isn't a good move - it's just I have some tricks in some of the lines.
What I'm not concerned is the result of the game, but how to result came about. I won't say anymore than that, as I don't want this thread to be locked.

I see where you are going.
You just need to have a glance at his statistics to see something weird is going on.
And what a nice "theoretical" preparation... Ben Finegold once said "Tricks are for kids".

Insinuations are just as bad as outright accusations, so locking. If you have cause for concern, report, don't post.
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I recently lost a rapid game against a player:
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