It seems to me you are a good mum already! The very fact you are so worried about getting things wrong and want the very best for her is proof of that. So please stop worrying about that.
If you feel very low and very anxious then, of course, you should see your GP or HV for advice, but much of what you have typed sounds to me like a very normal reaction to becoming a parent and reminds me of how I felt when my DD was small.
I remember finally plucking up the courage to take my DD to a mother and baby group when she was about 3 months old, taking ages to get out of the house, finally getting there, speaking to no-one and then coming home and crying my eyes out. But you know, slowly but surely (and after trying out different places) I started to make some really good friends.
I found the first six months (at least) with DD really hard in terms of feeling lonely, socially isolated and anxious about looking after her. I even bought her a present a six months to celebrate the fact I'd managed to keep her alive for half a year!!
If you do feel able to share some of your feelings with DH you may find he has his own concerns about how he is coping in his new role.
Oh, and please, please don't feel like a failure over the breastfeeding. I only managed six days and felt needlessly terrible about it for ages. It's natural to feel sad it didn't work out, when it's clearly what you wanted to do, but you have no reason to feel guilty.