UAmama, you shouldn't feel horrible at all.
The decision to have a baby can be scary whether it's number one, two, or five. Also, with a 10 month old your emotions are absolutely allowd to be out of whack. I had a lot of anxiety in the first few years of my DS's life.
I have a 3 year old, and we have been TTC #2 for 13 cycles. I knew I wanted another baby before DS could even walk well, but I absolutely wasn't ready right away. With you breastfeeding and everything I can absolutely understand how the idea could be a bit overwhelming. LO's are an all consuming part of day to day life, so the fear that you wont have the energy or enthusiasm for 2 is definitely not unfounded. I don't think not loving a new baby is something you need to worry about though, not that I'm discounting your feelings, just that your such a good mama you worry that there isnt enough of your heart to go around. I'm sure you'd love a new baby just as much, as you dont have a finite amount of love to give, in fact I've heard your love just multiplies exponentially with each baby.
I think we would have alot in common. My DS is 3 and we still co-sleep (though partially at this point because we are transitioning him to his own bed). I am also in my early twenties and would consider our lifestyle attachement parenting oriented. I have stayed home with my DS since he came home from the NICU at 54 days and pretty much held him at every moment possible, he follows me to the bathroom,kitchen (and pretty much everywhere else) and never lets me out of his sight.
I hope you can find some peace, with whatever you ultimately decide. (to keep trying now or wait a little and space things out a bit more). If you ever need perspective from someone who can relate to probably a great deal of what is going on/what your feeling or just someone to vent to keep me in mind. I think it's cool to find ladies in similiar situations as myself, or who are close to my own age. Keep your head up.