I've known him for 10 years (he'll be 22 in a couple of weeks). Birthdays are important to him, when he was younger I made him cakes, gave gifts. He would always congradulate me until an issue happened with his mother.
I'm not even sure what the issue was but I learnt later that she was talking behind my back to different people, I guess because she didnt like something and since she involved her son into all of her issues (not just with me), he decided to lash out at me for something that didn't concern him or his mother. It was very weird, but after a couple of years, he decided to apologize to have a good relationship as he said.
I would think that he remembered that my bday was a few days before his, but in case he didn't, my DP mentionned it the day before. And while his brother and sister congratulated me, he didn't. He's not one of these people who doesn't take birthdays seriously.
Should I take it as him actually not caring about a good relationship and just avoiding coldness that resulted in his own behaviour? Somehow I think that in a blended family that is not recent, knowing about someone's birthday and ignoring it is actually not a sign of a good relationship. And he does want my son (his half-brother) to love him and be close to him.