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Comment:

After having wrecked my first serious relationship with a great amount of pain on both sides because we both discovered our desires in the middle of it (both submissive/masochistic), I never again considered a vanilla (or submissive) person for a serious relationship.

My second serious relationship was (and still is) a Dom recommended to me by various (female) people. We are now together for 10 years, 6 of them married :-)

As for your question: Yes, I am sure (given that both partners are into BDSM and their likings/style fit each other) a BDSM relationship is prone to be more fulfilled than a vanilla one - and be it only for the reason that with BDSM you have an almost infinite variety of things to do, whereas in a vanilla relationship there are only a very limited number of things/positions one can try out.
For me, in a BDSM relationship
- trust is greater
- respect is greater
- excitement is FAR, FAR greater

As I am a jealous bitch, including a third person into our relationship for the purpose of "spicing things up" has never been an option. *grins*

Mind - I do not say BDSM is the cure for all relationship troubles. Of course you will have to care about each other and keep communicating as much as, if not more, in any vanilla partnership/marriage.

I hope that helped.

Kind regards
Arria