I'm invisible.

There are days and weeks I feel like I'm invisible. No one says anything to me unless I've done something wrong, I try to say something to someone else, and they'll talk to me for as long as I'm the only person in the room, then they'll stop abruptly and start talking to the other person, it doesn't matter if I'm in the middle of a word or not. I never seem to fit in anywhere. I'm often treated like I'm the most useless person on the planet. I've given up on socializing with anyone, because there's no point in it. I'm not getting it if I try or don't, so why should I keep trying?

There's no rule that says you should keep trying.

If you deem it pointless and you're ok with the alternative, then there's really nothing wrong with your decision to stop trying...

My two cheap words of wisdom:
Sometimes, without realizing we send subtle messages to the people around us that make them don't take interest on us.
It could be as simple as a lack of confidence on our posture or on our voice. And we can only change our atitudes if we change our mind frame. If you don't believe in yourself it becomes harder for people to trust you. Not because you are a bad person or not because you are not worth to know. It's just the image you present.

I don't know you in particular, so I am just speculating.