Ok, I know it sounds weird, but I'm afraid that if there's a DC2 I won't have enough time / love / emotional energy to split between them both (plus DH), and either DC2 won't get enough love and be neglected, or I'll feel like I've damaged my relationship with DS1. I know most people have more than one child and they all manage, but is it really REALLY possible to love them both and not feel like something has had to suffer as a result? I am truly mentallly in love with my DS1 and I can't imagine being able to feel that about more than one little person!!!
The background to all this is but this is I got pregnant with DS very quickly after DH and I got married. We were a very close couple, very in love, and excited about baby. But when DS1 was born I had terrible - T.E.R.R.I.B.L.E - PND and it was mostly because I felt he had "ruined" our relationship as a couple. I couldn't cope with the lack of time for us as a couple, the stress, the constant demands from this new person, etc. Basically, I just couldn't cope with two lovely people in my life!
Once I got over the PND things got much better and I adore DS with absolute insanity. RElationship with DH is very good but nothing like when we were first married because there just isn't enough time to devote to keeping our relationship strong (sex? evening out? relaxation? What's that?). I'm terrified of doing anything that would "ruin" my relationship with DS1, I could never forgive myself.
Sorry this is a bit long, it's hard to explain in a rational way.