What are the differences between Domestic Partnership and Marriage

Location: Oregon

My partner and I have been together for nearly 3 and a half years and are planning to get married within the next few. The only reason there he isn't my fiancé yet is because we have both agreed it would be better to make sure we have some emergency savings money together before worrying about buying a ring.

We are both 23 and early in our careers, and at the moment he is the only one with employer sponsored insurance. When I turned 22 I was kicked off my families vision and dental, but I'm still on for health insurance. I am also unfortunately a medical disaster and have multiple chronic conditions. One them affects my teeth and causes them to break down much more easily. Recently I have been in much more pain and I worry that I may be in danger of needing another root canal soon unless I seek treatment to prevent it, and I don't think we could afford it out of pocket.

Would I be able to be on his dental and vision if we entered a domestic partnership? As much as I know it would be easier we can't just do the legal part of the marriage thing, his family is far more traditional than my own and would be incredibly upset. Would I lose the health insurance from my family if we did enter a domestic partnership? I've looked through some of Oregon's law information regarding the subject but I can't say I fully underatand it, and I'm trying to understand what other ramifications it may have.

Thank you!!