I have always found the subject of marriage and people's opinions on it incredibly interesting. I have married twice and twice divorced and never plan to enter into any sort of legally binding union ever again. I finally realize that for me, that little piece of paper that means so much to so many is actually the beginning of the end for me. Bottom line, however silly, it makes me feel trapped and everything is downhill from there. What you have to do, and it sounds like you have already, is figure out what you need to do to make yourself and the ones you love happy. If being legally married is important to you, why? Are you willing to go about your life in a less conventional manner if need be? What is your truth?
My dad is a very traditional man and this is what he always told me, which is why I eventually caved and married my son's dad. He stressed how important it is when you have a child to have legal recourse if things don't work out as you'd hoped they would when you started your family. Ideally we will have picked a mate that is a good man and father and don't have that to worry about but I suppose he's right. Sometimes people we think are, aren't and sometimes those that were aren't anymore once the towel's been thrown in.
Think it out, journal, consider everything, then come to the best decision you're able to and be happy and content. Never look back or second guess yourself. This is a favorite quote of mine, just for grins...
"Among the maxims on Lord Naoshige's wall, there was this one: 'Matters of great concern should be treated lightly.' Master Ittei commented, 'Matters of small concern should be treated seriously.'"
Best of luck to you and yours!