I never even made the Thelma & Louise connection!
The sexual relationship is implicit even though it's not 'open' in that Polly takes it that Tonks is a boy at first (she's almost as good as Polly at being a boy) and that he's' Lofty's lover in that configuration. The Thelma & Louise corelation is entirely valid and far more appropriate (now I see it
) as those 2 women's core relationship equates to the type of 'buddy' relationship that's wholly sympathetic to a 'best-buddy watch each other's back' arrangement that soldiering is all about.
With Lofty being so fragile and damaged I think in some ways their lovers status is not that important to the central story because of her being so badly abused - in that situation I think that it's the protective, nurturing, almost motherly role that Tonks primarily displays throughout, regardless of the sexual side of it that's far more important and indeed absolutely feminine and sympathetic. That also applies to the buddy male soldiers connection, but it's far easier to see when we know they're both female