Got a new group email from a friend today planning her significant birthday for February, at a local place - obviously subject to whatever restrictions may be in place at the time...!
Leaving that aside, it's not at all clear from her message if she's inviting DP and I, or just me. She's not added DP to the group, but she hasn't got his email so couldn't. Of the others that are on there, the only ones to have replied so far have just said count me in - and I don't particularly know any of them that well so don't know if they are single or not. I know numbers wise it's quite limited (around 20). There are other people I know she'll be inviting who are in relationships but I'm assuming she hasn't got their email and is texting them.
I've not really spoken to friend much since pre Covid, I took a step back from our group around Christmas 2019 because I was fed up with being the one who organised everything (and in the past 2 years prior to this I'd not really heard from them other than a Happy Christmas/ New Year text or FB birthday message). I see the message as a bit if an olive branch, and I know DP will be willing to come along but I don't want to be the twat who replies and says 'we're both looking forward to toasting your 40th with you' and then find out it's only me who's invited 
As a follow on from that I'm assuming we all pay for our own meals? Is that usual?