Should I go this party?

I've been invited to an old school friend's 21st birthday party. Most people wouldn't think twice about going to such a thing but I am feel very unsure about whether to go or not.

I haven't seen this person since I finished sixth form three years ago. We were good friends in school, hung out at parties, invited each other to birthday events etc but we lost touch after we had finished sixth form. I think this was because it was just me putting in all of the effort to arrange a meet up and they didn't do anything to make it happen. Also, my 18th birthday party was not long after we had finished A Level exams (I have a summer birthday) and they didn't come to that, even though I went to theirs.

So I was surprised when they invited me to their 21st. It seems like this person has also drifted from everyone else that they were friends with in school. So I am wondering whether the likes of myself were invited to simply bulk up numbers?
In addition, I don't know most of the other guests. The only ones I know are some people that I went to school with, but I wasn't close to them at all and I find them to be a self-centered and fake.

Should I go? It would be nice to see my friend again, but if we haven't met up since leaving school and no effort has gone into arranging something, doesn't it kind of suggest that the friendship wasn't that meaningful in the first place?
It also seems like they might be the type of person that wouldn't return the friendship if that makes sense? Like, if I was to invite them to my 21st, I doubt they would come.

Any advice on whether I should go or not would be greatly appreciated! Thanks!