She’s not unreasonable to want to see you every weekend, but she’s unreasonable if she expects it - they’re two quite different things.
I’ve recently separated from my husband and yes, I am lonely because many of my friends aren’t very available (marriage/kids). In fact, I’m desperately lonely at times and if there was a friend who I was close to I might want to see them every weekend at the moment even though that’s not my ‘natural’ state per se.
However I don’t expect anyone to be that available - and they aren’t.
It’s up to you to set boundaries that work for you and your availability - if she invites you to do something and you feel like you’ve seen enough of her lately and want a break, then politely decline.
If she has a tendency to turn a coffee into a four hour chat and you don’t want that, then say in advance “Would love a coffee, I have something on later in the day so can only stay until 2pm”. Then leave at 2pm.
It isn’t your friend’s responsibility to manage your boundaries for you, only to respect them when they’re set.