I understand. Thank you for telling me more about your situation. It helps me to give you a better answer.
Yes, we can focus on you. It is actually a very good thing that you want to do that because often times, people will try to change their partners and that is very difficult to do.
How do you feel about leaving the situation whenever your boyfriend needs to deal with his ex? For example, when she is supposed to get the kids or have contact with your boyfriend can you have something planned like a couple of hours out with a friend? Giving him space to deal with his issues will keep you out of it and therefore you will feel less stressed.
Take some time with each other that is special and away from the drama of the situation. If you feel it would work, try going on a short getaway. This is for the intimacy as much as it is to deal with the the stress
of coping with his ex.
There are also some books that may help you. Although they are mostly for someone marrying their boyfriend, they have good tips and ideas for your situation as well. One is called Ex-Wives and Ex-Lives: Survival Guide for the Next Wife by Paula J. Egner. Another is How to Marry a Divorced Man by Leslie Fram. And another one is The Single Girl's Guide to Marrying a Man, His Kids, and His Ex-Wife: Becoming A Stepmother With Humor And Grace by Sally Bjornsen. You can find these on Amazon.com or your local library may have them for you.
Be as supportive as you can, but also find ways to help yourself with the stress. Go out with friends, get a massage, see a movie, take a day off and just go for a drive, learn yoga or meditation
or other things you find that help you feel relaxed and happy. It is hard when things are out of your control, but remember, this too shall pass. One day (very soon!) the kids will be adults and the ex will no longer be in your life as much and will no longer have any control over your schedule. Take a deep breath and keep in mind that you have a wonderful boyfriend, a great relationship, and much to look forward to.