Should I just give these friends up?

umm... yeah that's hard. Sometimes I feel that way too, but the way I deal with anyone whm I've upset is to shut down. They probably deal with it the same way. They might not invite you because they can't approach you, or they forgot to, or something. I'm sure they didn't forget your birthday on purpose, heck, sometimes I forget MY OWN birthday! If you haven't known them forever, then give them a few more years to bond.

Sometimes, all it takes is a little heart-to-heart. Just say what you are feeling. If they don't do anything after that, THEN you should think about breaking off the relationship because they obviously don't care about you enough.

If you really want to, the best way to let go of friends is to occupy yourself with something that doesn't need those specific people.

Like making new friends. This way you won't really know you are drifting apart.

Sadly this works...

Thing is, speaking from experience here--a group of friends do have a dynamic.

Just as in algebra an x factor.

Where one person or individual fits in--is going to indicate what occurs in this group setting.

There are a+b-cx2 etc

So don't be surprised about this--once you figure which you are--then accept it and move on or out and form your own group where friends are not excluding group members.

Not very nice feeling this exclusion of members.

It is what it is--political sad to say.

Exactly: you need to be yourself.

Friendship is unconditional and accepting each person for their individual flaws and good habits etal.

Same thing happening to me. I am trying to give up on my friend who hurt me and just ignores me, but I can't.

You stop going to them when you feel lonely. If they've forgotten your birthday, they definitely shouldn't be your friends. Try to find a new backup. Still be kind and friendly if a conversation is bound to happen but don't purposely start one.