Some background. I have a friend "Sam". When we go out, we normally just pay for our own meals/drinks/coffees, etc. However, there have been a couple of occasions in the past where I've taken Sam out for her birthday, and paid for both our meals (and movie tickets on one occasion). Sam doesn't really reciprocate when it's my birthday, but that's only because I normally choose to celebrate my birthday quietly with my partner instead, not because of any failing on Sam's part! (Sam herself is single, so doesn't have a partner to celebrate with).
Yesterday we had a conversation which can be summarised as follows:
Me - "Hey, there's a great new little restaurant on ABC Street. We should try it out sometime."
Sam - "Yes, that sounds lovely. It's my birthday in a couple of weeks. Let's go there to celebrate!"
Me - "Sure, sounds good."
Now I'm wondering: based on past practice, did I put myself on the hook to pay for Sam's meal and drinks here? I don't mind, as I can easily afford it, but I'm wondering what the etiquette is in this situation? Should I offer to pay for Sam? Would it look churlish if I didn't? Or do I attend with the mindset that we'll be paying for ourselves?
(Note, if it makes a difference, we won't be going on Sam's actual birthday as it falls on a work night, but rather, a few days later on the weekend.)
(Note 2, Sam and I don't normally exchange birthday gifts, so that's not really a factor here.)