@Lewlew,
You do deserve better.
You spent your big relationship-forming years with someone who didn't appreciate you. You allowed him to prioritize someone else over you. You allowed him to take you for granted.
Imagine 30 years like that. It's not a pretty picture.
Get yourself some counseling (I am not a doctor). Get some tools for enhancing and shoring up your self-esteem.
Yes, it can be scary to upset the status quo. But the status quo sucks. It won't change until YOU are the one to force the change.