As for your kids, and W actions, figure out now how to act in that situation so that if it happens again you have a plan. I agree with protecting the kids from that behavior.
I am not sure why you helped buy the car, if your separated in a Separation agreement the assets will have to be split up, you will have to sell the car and get you off the car loan. I imagine though W has not talked about a separation agreement yet?
If not you are going to have to master the ideas of boundaries and setting them and enforcing the consequences of W breaking them..
With in house separation and no parenting plan, who looks after the kids is up in the air. You need to plan on activities for yourself to be out of the house so your W does not just only leave you to look after the kids when she is gone, you need to balance it out. Its called GAL activities.
The other thing you are going to have trouble with is finances. She will spend your money like you are not separated. You need to have your own money to spend how you want. Also it was hard for me but you need to go see a lawyer just to get the fear of that out of the way.
keep posting.
Me late 30's W mid 30's T 15, M 10 S4, S7 ILYBNILWY June 2015 In house S July 2015 W rings off Oct 2015 My ring off Feb 2015 Separate houses June 2016