AITA: 50/50 shared care with 0% financial care

Alright folks...I need your objective opinions - this is an emotionally charged situation for me, so needing the thoughts of others completely detached from the situation. Bare with me whilst I provide the background details.I'm a working single parent to one child (5yrs). I have been separated from my ex-husband since early 2015, with divorce only being finalised in 2018. I have been the primary carer of our child since separation. I have also been the primary financial provider for our child and continue to be.My ex-husband is demanding 50/50 physical shared care of our child, and is threatening court if I do not grant it.I have always been encouraging and protective of the relationship between my ex and our child - they both have the right to a continued positive relationship and it's in their best interests. There are no concerns regarding child safety in this case. Our child also now has a Step-Mum whom I regard highly, and I love that our child has another positive role model in their life that loves and cares for them.Am I The Arsehole for being exceptionally hesitant in agreeing to 50/50 care on the following basis:My ex-husband earns a minimum of $96,000per year (Aussie dollars). This minimum does not include cash earned on the side (he's a tradie). He works full-time and is the owner of a business he and I set-up when still together, of which is highly successful now. He has a "declared" gross taxable income of $36,000. He switched the business from "sole trader" to "PTY Ltd/Company" , so despite earning a minimum of $96k, he draws an annual wage from the company of $36k. Perfectly legal here in Australia. He has significant assets also.I, on the other hand, work part-time (whilst also completing Post-Grad studies) and have a taxable gross annual income of $48,000. I walked away from our marriage (getting out of there was the priority), requesting nothing financially and allowed him to keep everything financially.My ex currently pays very nominal child support. I provide financially for our child in every way, including extra-curricular activities, medical care etc. My ex chooses not to provide financially in this area as he does not want to part with any money.If I were to agree to 50/50 care, I would then be in the position of having to pay my ex-husband child support, as the tax office sees on paper that he earns "less" than I do. The amount of child support I would need to pay him would mean I can no longer financially afford to provide our child with extracurricular opportunities and other needs...my ex will not contribute financially even with 50/50 physical shared care. There are many opportunities our child would miss out on as a result, because I would not be in the financial position to afford them.AITA for being very hesitant and disliking of 50/50 share cared in this instance, based upon what would be my inability to provide for our child as a result (meaning a loss many opportunities and basic necessities)?Be honest folks...Have I lost my shit or is this a reasonable concern? via /r/Parenting https://ift.tt/2Luod0M