Taking a backseat to adult children

I'm early 60s and in a new couple month old relationship. My significant other has 2 children late 30s who are married and on their own. I have been told and shown that they will always come first. I dont need to always be first, but I would like to feel like I am not always 3rd place. Everything else about the relationship is good. Should I move on or wait it out hoping for it to get better?

In what ways has he shown that they come first?