I was reading the lyrics of a song called "Dominoes" by Syd Barett, and couldn't understand what he was trying to convey in this verse "Losing when my mind's astray"
I do not know the song but I think if you consider it literally: He is playing a game of dominoes with his girlfriend but is pre-occupied with their failing relationship - his mind is on other things [gone astray]. As a result, he is not concentrating on the game and, as a result, he loses.
It could also be a metaphor for their relationship - perhaps he has not been paying his girlfriend much attention, possibly looking at other women - playing another game... and, as a result their relationship is failing and he is losing her love...
Go astray: Wander off the right path or subject; also, wander into evil or error.