Lots of advice here from mums who gave up work. Actually 70% of professional working mothers do return to work within the first year. So if you would return, you would certainly not be alone.
All research I have seen suggests there are hardly any negative consequences to children when both parents work. It is very key though there is a main carer that your baby feels safe with and loved by. Many parents I speak to actually tell me that when they are teenagers they need you most. ('anyone could do the babycare, but teenagers do not a lot more input'). This is not to dismiss anyone who is brilliant at looking after a baby, just to show there are different perspectives. The key thing research says: if the parents are happy, the children are. So if you are going to feel guilty and fret about leaving your child, they will know. If you are going to be at home and become frustrated and depressed, they will know. Do what feels right for you.
In my experience from talking with many parents, you will only be fulfilled as a stay at home mother if some of the 'drudgery' that is part of it you really enjoy: looking after a baby, arts/crafts, cooking, or being part of the baby-voluntary circuit. The only way to really know is to try it out, of course. But in your case that sounds really hard to do.
Perhaps it helps to look at my website, as there are a lot of stories on it from working mothers (
www.mumandcareer.co.uk) and lots of help for how to make it work.
Personally I believe it's always sensible to have your own income, but not everyone agrees, and it depends on the 'price you pay', which is very personal. A jobshare sounds fantastic, though. You may not easily get that somewhere else.
And indeed there is a biological aspect to having a baby. Your hormones are all geared up to bonding, and nesting. It does take some effort to overcome those powerful urges, and it really helps if you really do love your job and genuinely enjoy working, and know why you do it.