Hello OP, and congratulations
Just to echo what others have said, what you are feeling is totally normal. But i always equate it to learning to drive or acquiring any new skill. At first it's scary, challenging and you over-think everything, but after a while it becomes automatic and one day you realise that the new life you have is so much richer and more fulfilled than your old life and you no longer yearn for it. Of course there will still be times when you think back and remember what you and your OH did prior to your DC and a little part of you will miss it, but those thoughts will be fleeting. My advice is to try to stay as true as possible to the people you were before: if you used to go out on a Friday or Saturday, then continue to do so. Your choice of venue might change, but young babies are so portable that you will probably be able to enjoy a drink or a meal together while your baby sleeps beside you. I'm a firm believer that life does not have to become unrecognisable to the life you had before when a baby arrives, you just adapt a little. We booked a weekend away when DS was 8 weeks old, went for walks out, meals and drinks. Even went to a music festival! Everyone told us we were mad to do this when DS was so young, but i'm so pleased we did it - it made me realise that i was now a mother, but was essentially the same person. Do try to get out as much as possible, though i understand that's currently difficult and sore for you.
I remember missing just being able to nip out to the shops alone without it having to become a military expedition. Life used to be so simple! I also remember after a particularly bad day in the first couple of weeks thinking "Sod it. I'm going. I'm leaving DH and DS and i'm never coming back." The thought disappeared almost as soon as it entered my head, but i will never forget feeling that way for a moment.
Have you thought about seeing whether you can afford for your DH to take another week off work, perhaps on unpaid leave? At around the same time as you my DH was due to go back and i remember being in floods of tears, not ready to go it alone just yet. I felt an impending sense of loneliness because i was not ready. He took another week off and that was all it took for me to be feeling more like my old self again. I think i had a pretty rocky start for those first few weeks because i had no confidence in my own instincts, but talking to friends i think that after that i took to motherhood much easier than many of my friends who were still struggling after a few months.
The only other thing i will say is seek help if BFing is not going well. While it's totally normal to take time getting to grips with it, if you feel they are problems you are not overcoming, speak to someone. I wasn't sure that sore nipples was 'normal' at first until i spoke to my sister, she gave me some cream, and after a while it was much better. I carried on BFing till DS was 9mo but i appreciated talking to my sister who had been through it.
Sorry to sound preachy - just wanted to say that you're not alone and have so much to look forward to. DS is almost 2 now and a wonderful, happy, funny, active little boy. And we have grown as a family and i am a better person because of it.