I would consider the car a family car. We have a car each, but if one breaks, we would work out how to share one for a day or so.
Totally agree - surely that's how families work, isn't it? Technically, we each have a car in our own names, but in reality, we have two family cars. The clutch went on 'mine' (the bigger one) just as we arrived back from holiday and we don't have the money to fix it yet, so it's temporarily out of action. Therefore, for the time being, we're both sharing the smaller family car and whoever's need is greater (getting to work etc), they take priority.
Same with earned money and inheritances - why wouldn't you consider them family money if you're in a secure marriage? If it's a lot of money, the likelihood is that it will be spent on something that will ultimately benefit both adults AND the children too.
Men who earn the money whilst their wives are SAHMs of their young children and use that to control her are disgusting, as her valuable contribution is mainly to care for and bring up their joint children - but that doesn't mean that any money that comes via her is therefore automatically hers alone, any more than it means he should automatically never be expected to do any mundane/unpleasant childcare-related tasks in the evenings or weekends.
Money given for a specific purpose is different, though. If OP was crying non-stop and genuinely in pain because of the tummy issue, and her DF offered to buy her an operation to fix it, take the pain away and get her back on her feet again, then of course she should use it for that. Especially as any pain or discomfort caused as a direct result of the pregnancy was related to their JOINT baby.
However, if OP is in a bad place and was crying because life is getting her down generally (maybe also her DH), so her DF offered some money to try and make her happier, to spend how she saw fit - and then her thoughts instantly turned to things specifically for her rather than things that might benefit them all - that's a much greyer area.
I hope I'm wrong, but going on the attitude expressed about the car and any inheritances, I wonder if the OP is wanting to retrain to enable her to work and earn money solely for herself (as SHE has earned it) whilst her DH is still expected to earn all the money to pay for the whole family's needs.