Expectations re birthday lunch... is it me?

[DanceDanceRevolutions]

My mum had a big birthday recently and for part of her present DH and I offered to take her out for a fancy dinner.

Think high-end £100+ ish a head type place. Not the sort of place we would usually eat at but, as I say, it was a big birthday.

There were six of us; me DH and our two DC; my mum and her husband. When the bill came I had expected my mum's husband to chip in and cover his share, leaving me to pay for my mum and the rest of my family... but he didn't. He had assumed that me treating my mum meant me treating him as well.

Was I in the wrong here for assuming that me offering to treat my mum meant covering her dinner and not his too? (And yes I should have been more explicit; I know that now! I just paid the whole thing and smiled rather than have any drama at what was otherwise a very nice family meal out)

'DH and I offered to take her out for a fancy dinner.'

I wasn't expecting to read the thread and find there was a group of 6 for this dinner.

but as you ( and dh ) were paying for 5 of these 6 people, of course you pay for all six.

did her husband invite himself, or did mum invite her husband or was it just assumed that her husband was invited

People don't "come as a pair"! Each person is an individual. I hate this notion that once someone is in a relationship they merge into each other and cease to be their own person.

You don't buy your dad a mother's day card as well as your mum,
You don't buy your dad a present on your mum's birthday.
You don't buy your dad a new lipstick just because you got your mum one.

Etc.

I agree that OP should have clarified it earlier on, but decent people recognise that one person's specific birthday treat isn't a freebie for them to muscle in on. Sadly it sounds like the stepdad is a dick so this didn't happen either (and as previously commented, it could have been done discreetly/behind the scenes/after the event, no drama at all).

If it was a birthday treat for my mum I wouldn't expect her to take it literally and leave her partner behind. Just like I wouldn't expect to invite my son out for a birthday treat and leave my DIL out of the equation. I equally wouldn't be paying for everyone else round the table but be holding my hand out for my DIL's contribution.