i know they are going when one of them post on facebook

to be honest if they ask me to go, i will prob see what is the
destination first before deciding. The thing is, i don’t have many
groups of friends to go travel with. I do have another group of
ex-poly gal frens but those are mainly for dinner and drinking the
night with. I dun feel particularly close or itimacy with them and
i think they also feel the same way too.
I got 2 more frens from my part-time degree course and 1 of them
has her own travel buddies/frens. Another one is ok, i did
travelled with her to places like NZ, HK etc but she recently
change new job after unsuccessfully trying to be property agent.
Plus she is getting married soon and just got her new flat. So I
know while she donesn’t mind travel with me, i koe she really needs
to watch her finances and so i dun think i will ask her to travel
anymore, at least not for time being. And throughout my whole
working life, for some reason i have only manage to meet 1 or 2
girlfriends of similar ages whom we can go out for dinner, drinks
and movies etc. But i find that after sometime like i left the
company or one or the other change jobs or got married, the meetups
got less and less frequent. And it does not help that i tend to
work in those companies where there are always foreigners or other
type of demographics of people (eg much older women with teenage
children). I also try to look for some gal frens to hang out, and
have fun. Other pple seem to find and clique with people easily. In
fact, my this group of frens they also have each of their own group
of frens and buddies formed by ex-colleagues or school mates etc. I
dun know why it is so hard for me 
and the fact I know them for 20 years and they just went ahead
to make plans without even checking in with me
So you had your travel buddy, but she is no longer available.
And when you traveled with your travel buddy did you ask any of
your 20 years long friend to come along ?
Now that you no longer have a travel buddy, you become upset
your other friends didn't ask you along. Yes?
It seem you are not very close with these 20 year long
friendships.
You should be able speak up/out about anything on their mind to
a close friend. Like a simple " where are you girls going ?
"
But you don't seem comfortable to do so. Instead u pout and get
mad they didn't ask you.
They are more like 20 years acquaintances.
It's time to rebuild, restrengthen, re establish friendships
with people you care about.
Perhaps a little less pettiness will help in your rekindling of
old friends.