My DD (11wks) is my 3rd child, although I have only ever had 2 children to care for at any one time as my eldest died of cancer before my 2nd was born. My DS will be 3 in March and when we tried for our 2nd I got caught straight away which shocked me a little (I know it shouldn't really should it?) because I was expecting it to take longer (I am nearly 40) and thought it would give me more sole time with my then 2 year old son - this was particularly important to me as I work full time and started back at work when he was 6 weeks (part time) and then went back to full time when he was 12 weeks.
I think during my 3rd pregnancy I seemed to worry less about whether things would go ok - but maybe this was because my 2nd seemed incredibly precious having already lost a child - I don't know?
I worried about how I would split my very limited time and be able to enjoy both my children. I thought maybe I was selfish to want another when I worked full time anyway - my DH is the one who stays at home as financially that worked better for us.
When I went into labour I ended up having an EMCS after 3 hours in advanced labour for a life threatening event with my DD and we were told we were very lucky that she was, because of this, delivered healthy.
When she was nearly 3 wks old she developed silent reflux and screamed all day long and kept my DS awake until about 11.30 at night - it totally disrupted our lives! Despite this my DS absolutely loved the baby and was so good with her we could not believe our luck! Like yourself he was absolutely the centre of our world and everyone heaped so much love and attention on him that I was worried about how he would cope with someone else to take some of this away from him.
Once she started on meds for this she was like a different baby and is now very happy and he continues to enjoy her and her him - her face absolutely lights up when she sees him.
I think what i'm trying to say is that even if your son does have some disruption when this baby is born I am sure that you will manage and that overall it will be a positive experience for him and for all of you. Together they will both give you delight and you'll have all those same lovely feelings for DC2 that you get with DS1.
Continue to enjoy your DS now but don't worry that this will be the end of the enjoyment.
I hope all goes well for you all and that you can stop giving yourself such a hard time.
Take care xxx