Momai, I have the utmost respect for anyone that is a single parent. My mum was, and I really had no idea just HOW hard it must have been until I had my daughter. My husband goes away a lot, usually about 50% of the year he is away (although in slots of several weeks at a time) and each time he goes away I struggle so much and always think how amazing single parents are.
Also, I don't know if this helps or not, but I was a blubbering mess around Aliya's first birthday, and I had lots of family around (incl. Mr S). Having spoken to several Mummy friends, it seems that a lot of them also were very emotional on LO's 1st birthdays, remembering back to "this time last year" is quite an emotional thing I guess!
I'm not saying that to detract in any way from how you are feeling, but wanted to reassure you that it is a very normal feeling.
I hope that you are ok. 