Now that he's remarried, can I still count on my ex for help?
Co-parenting issues are important to discuss with an ex husband, but it's wise to distance yourself from an ex who has remained an advisor about work, finances, travel—topics other than the children. This is true once he is remarried, but also if he's not remarried. Otherwise, the boundaries are blurred. This could upset, maybe even infuriate, his new wife, and it will keep you from getting along without him and from forging new relationships and your own sense of independence.
The second wife is likely to resent that you lean on him and might make matters difficult for your children as a result, or she could simply ask him to cut contact with you. Then he'll feel torn, and your children might suffer. It's best to have clear boundaries and avoid becoming a triangle of you, your ex husband and his new wife. The triangle can lead to competition between you and the second wife and will make life difficult for everyone involved.