I wanted to reply because I can understand the guilt you are feeling. I FF my first two DD. But it wasn't easy getting there.
With my first, I started out breastfeeding. It did not go well. She had a tongue tie and wasn't diagnosed and treated until 3 weeks. During that time, I had terrible cuts and holes. It was awful. I would cry in anticipation of her waking up and wanting to eat every single time because of the pain. And then after feeding her through incredible pain and tears, I would sit and pump and not be able to hold and cuddle her. Finally my mom, who BF me and my sisters stepped in and told me it wouldn't be the end of the world if I FF fed her and that the stress was ruining time I should be bonding with the baby. That maybe FF would better for my relationship with my baby. I decided to switch, but I still had so much guilt that I was not giving my baby the best. After making the switch, it was sooooooo much better. The stress left and the bonding with my baby got much better. It was like a weight was lifted off my shoulders. She is almost four now and thriving.
With my second, she ended up in the NICU right after birth and the nurses gave her formula right off the bat. I started BF again, but I couldn't keep up with her demand. So I nursed her and supplemented with formula. Eventually I dried out and she was EFF. This time around I knew that she was going to be ok on formula and had a little less guilt.
With my third DD now I am EBF. I have to say, I enjoy FF my babies much better than BF, but I wanted to give it one last effort. It may be the lingering issues from trying to BF my first two, but I just don't enjoy it and am stressed and frustrated by it.
This is extremely long winded, but I just wanted to let you know that no matter what your story is when you decide what is best for you and your baby, you will know right away that it was the right decision because you will not be stressed out and things will fall into place. The guilt will also melt away when you realize that your baby will be just fine on formula. Be proud of yourself for making the right decision for your family. GL!