Don't let it get to you. If he truly and honestly was sick, then you probably should give him a break. Then again, if I were sick and I was with someone that I'm in a relationship with, I most definitely wouldn't forget it at all. I would look forward to that birthday. Maybe talk to him and ask if there's anything else he has in mind.
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FUCK YOU. HE PROBABLY DOESNT GIVE A SHIT. YOURE PROBABLY A WORTHLESS PIECE OF CRAP GIRLFRIEND ANYWAYS.