Happy Birthday. I know this isn't the happiest birthday for you but I promise you that you will have better birthdays in the future. If he has left you again, on your birthday, you know what you need to do to make your life 100% better.
Figure out a game plan and don't have second thoughts this time around. He will only screw you again and again after promising you the world. Give yourself the best birthday present that you possibly can and get rid of this guy who thinks so little of you, he can't even remember your birthday. Or worse, he did remember it was your birthday and chose to not come home!
He is a Loser. You are not. Time to throw away the trash...
"Your value doesn't decrease based on someone's inability to see your worth." -Unknown Wise Person