This is all very tricky stuff, I've been caught up in this one more than once.
Its tough with kids ... and the WAW/WW knows ... at least mine did, call it mind reading but the WW/WAW can manipulate things to go their way and they will certainly use the kids to gain advantage ... least mine surely did. I am not saying yours did but I do think the point being driven here is be mindful of the situation as its very easy for both sides to say "its for the kids" ... especially you, Your W fired you and with that comes the responsibility of being a single parent, this is the life she will live, the results of her choice right? Bailing her out 'for the kids' can work against you ... but so can not being there and making sure your kids are take care of. You have to get to a place where you do these things not because of her .. but because of you.
I see the fact you fixed the car something you would have done for her, or someone you lived next to. Just an act of goodwill ... if you can stay in this mindset you are on the right path ... however if you fixed it and in your mind you tell yourself "see she needs me" or as you said "I will not be her maintenance guy" showed a bit of resentment and maybe you had some expectations after will bring only bitterness and not get you where you need to be ... think big game here, not just this one play.
Personally I found myself doing things for my S, as a way to show W what a great father I was but more so to 'win her back' thinking if I proved I was there ... she will have a change of heart .... inadvertently I was spoon feeding...heck shoveling cake. Not only was I living the single parent life on my own ... I was also the on-call step in babysitter/care giver/provider for W . Once I cut that and picked my battles there (Asking myself BEFORE I acted ... Is this REALLY for S, or for W?) ... reality started setting in for her, not only was she losing her H (this was her choice) she also started noticing that she was eliminating S's father 50% of the time and SHE had to pick up the slack I always held.... and No one .. not OM, OM2, 3 4 ... keep counting ... could EVER be the father I am. This is where you are the prize, the total package.
