An invented girlfriend as an excuse to say "no" is in no way LESS of an impediment than an actual jealous girlfriend?
Your partner's ex, your partner's friend group, your partner's life choices are your partner's job to manage.
It's okay if someone you strongly dislike gets an inkling that the feeling is mutual.
There is "what might be technically owed" and "what is realistic and workable now." In general, don't try to extract the former at the expense of the latter with people you'd like to stay friends with.
Let's you and me drive a stake through the heart of NiceGirl™ Summer.
When fear of over-committing meets terror of letting other people down, that's where you'll find me and way more than one of you, if my inbox is any indication.
Here is blanket permission to not worry very much about offending people who neither show up to your parties nor ever explain why.
Good fences continue to make good neighbors, metaphorically and literally.
"Dear Captain Awkward, how can I find out if my crush likes me back?"
Nature is healing!
There's a lot to be said sometimes for faking it until you make it, but I'm a big fan of dropping the act and dropping the shame right along with it.