My daughter is almost 23 mos and my son is 3 months now, and i love the two of them so much. I too wondered if i would have enough to give to both, but you will be amazed at how much love you do have for another child.
I come from a family of 3 siblings, where I'm the oldest. I grew up pretty much raising my younger siblings as my mom worked alot. In adulthood now, my brother and sister and I are still really close. Although we have had our blow out momemts (especially my sister and i are very different personalities and viewpoints) I know I can count on the two of them more than anyone else in the world. My mom would tell us pretty much on a daily basis growing up that we had to be each others' best friends. So I always thought you give your children a gift when giving them a sibling. And in the back of my mind, I always wanted 3 kids.. Of course the reality is I am more than overwhelmed right now with just 2. So I may very well quit now.
Havig a second kid, especially when your first is still a baby is and continues to be a big adjustment. It's a big lifestyle shift - even from having one kid. Where I used to have some semblence of "me time", it is now that much harder to come by. My husband and I always have a kid in our hands. I'm tired all the time, trying to lose baby weight. Wondering how I will go back to work with 2 kids in full time daycare. Financially things have never been this tight...and we have a new little person to pay for. The main things to ask yourself is can you and your partner step up and handle the additional responsibilities - time wise, financially, etc. Your relationship needs to be really strong to handle it. If youre both having a hard time handling the one, sharing the responsibility, etc. or the woman is doing most of the work, then having the second kid isnt going to make things better.
On the other hand -- my little boy is so awesome...truly a gift. My daughter loved her new brother from the first moment she laid eyes on him. She is a very loving big sister, alway giving him kisses and hugs. And he reacts to her (and to everyone) with big smiles. We prepared her for the birth by reading a picture book called "I'm a big sister" since she was about 1, and i think it really implanted in her mind that this would be a positive exerience. I know for us - our little "accident" turned out to be a beautiful blessing in the form of my smiling, gorgeous son. He is also a really great baby...He has slept through the night since about 8 weeks. I put him to bed now and he almost falls asleep on his own. I really cant complain in that area.
The other positive thing is you gain so much confidence in yourself as a mother (and jointly as parents) and there isnt nearly as much fretting and anxiety the second time around. For me, doing things for the second baby was almost by rote, as I knew what to expect more from the pregnancy, birth, breastfeeding, etc. and had all the baby supplies from my daughter still here.