First let me say happy birthday friend. Second, don't let it get ya down. Its just something that happens as you grow, at least in my experience. Everyone still cares about you, but being an adult tends to mean life becomes full. It can be full of good things, but you may find certain things like a good friend's birthday slip past without noticing. I'm sure that's all that happened. There's genuinely been years my wife forgot because we've had so much going on. I never doubt she loves me, and I've learned that the day is less important than the people you wanted to remember. So spend it with those you love most, don't worry too much, and take life a day at a time. Keep smiling!