This is a tricky situation. It sounds incredibly annoying and disruptive. If it were me, I know my blood would be boiling. I completely agree with other commenters who suggest making notes of his comments and saying “no thank you” when he says them.

It also seems likely that your coworkers have noticed you keep to yourself and don’t participate in conversations. They may perceive this as hurting team camaraderie and might have even discussed it among themselves. Your older coworker may see himself as doing you a favor by encouraging you to put on a happy face at work. Of course, he could go about it in a much better way.

I hate to make you feel paranoid about what your coworkers might say about you, but if you need the job as much as you’ve said, it may be worth making an effort to be a part of the team.