If you read that 'Scottish wild adventure' passage in TWS with that in mind, the dynamic (obsessed, drunk-on-his body 20 year old SW, unusually sheltered and who has never been away from her parents overnight before, who will literally do anything to be with a comparatively unconcerned TW, who is more focused on doing what he wants on holiday) is very clear, and accepted as normal by them both.
The Spanish girls at the campsite after the first day when TW bounded ahead up up a mountain while SW struggled after him ('I couldn’t give in, couldn’t be that whingeing, whimpering girlfriend and ruin his longed-for trip') are horrified by her bloody shoulders, rubbed raw by a too-heavy rucksack that TW borrowed from a friend, and unimpressed with TW:
‘What sort of boyfriend is he? Making you drag a weight like that about.’
The Spanish girls were crowding round looking at my dismal shoulders.
‘I wanted to come.’
‘Ha, really.’ They took the sponge off me and slowly and carefully bathed the raw skin, picking out the threads of green shirt.
‘It’s not my rucksack – I borrowed it. It doesn’t really fit me.’
‘Never borrow kit for the hills, it always causes pain.’ They smoothed the skin down with antiseptic cream.
No indication whatsoever that TW feels any concern for her, either struggling up a mountain after him or her injuries (which he can't have avoided seeing, as SW walks back to the tent without her top to let the air get to the wounds), or that she might not want to put on the same rucksack onto raw shoulders the next morning.
Seen like this, the whole 'mystical night in the plastic bag' episode is a desperate attempt that she may even believe herself to make a trip with someone unsympathetic, and who is auditioning her as 'outward bound girlfriend', sound like some kind of fated blood bond.
Is she still trying to please him, years later? Is that what all the thefts are about? He's a free spirit and she's stumbling along behind him trying to make sure she's not the 'whining, whimpering wife who is ruining his wild, free life' or something?