How to still get an invitation?
Make sure that the invitation from the other really did not. Check your social media accounts, e-mailboxes and see if there are any missed calls or messages on your mobile phone. Perhaps, each chose an unusual way to invite to your birthday and you missed the invitation. Talk also with those who the birthday boy invited to his feast. Find out how they got their invitation.
Perhaps, the birthday boy didn't call you a birthday because you are his close friend and need no invitation to this feast. If you communicate well and don't Harbor any hard feelings on each other, just try to come to him on his birthday along with all the guests. It is unlikely that he will be against it.
Whether to be offended by another?
Sometimes friends can test each other's loyalty. Maybe your friend wanted to see if you remember such an important date as his birthday, and coming to congratulate him without a reminder. If you doubt that it would be appropriate to come to him without an invitation, call a friend and congratulate him with the holiday. Ask how he is going to celebrate the celebration, and ask permission to not attend it. Maybe the friend just too shy to invite you and waited until you start talking about it.
Remember, whether it was between you and any disputes or quarrels for the last time. If you are guilty in something to another and asked forgiveness for it, he could keep the resentment and "revenge" that does not call you on your birthday. Maybe it happened even on his last birthday, and since then he has lost the desire to invite you to such events. Call him or visit in person, apologizing for any offense. Most likely, the friend will be glad to reconnect with you and invite to the feast.
In any case, do not quarrel and do not clarify the relationship with the other, if he never invited you to his birthday. If you value your friendship, do not put a cross on it because of one violation of human rights. Maybe it was his reasons that he just can't call. It is best to continue to communicate as before. And don't forget to invite a friend on your birthday. Perhaps he will remember that at the time, forgot about, and in the future will not allow such an error. While you will be appreciated for your kindness and ability to forgive offenses.