I feel stuck.. What do I do?

You are just going to have to suck it up. Your kids didn't ask to be born to you and your ex and they certainly didn't cause you two to split up. Those were grown up decisions that they are paying for now. You don't get to be immature about when and how you get to spend time with them. You just get to suck it up and make sure that when they are with you, you are completely present and lead a great example by not trash talking their mom (even if she does it to you). You owe this to your children. If you are overwhelmed by spending an entire week with them it is time for you to lean on whatever support system you have (parents, siblings, friends... whatever). And might I mention that your ex must spend weeks at a time with them if you are only getting them a few days and weekends and she makes it work. Being a parent is a full time job, even when you are divorced. It is your number one priority and should not be considered an inconvenience.