If you wanted to cover your butt, you could put a POA in place so your BF CAN legally sign (as your proxy) when you are not available.
I don't have any moral problem with a committed couple that chooses not to legally sanctify the relationship, but I will point out that getting that piece of paper provides lots of protection to you, him, and the kids, that you don't get without it. The legal issues are totally separate from the moral ones and there are legal advantages to being married. Just something to think about, in a totally non-emotional and non-judgemental way.