Frank assumes that he and Matt are soulmates, and doesn't find out until years after their first meeting that they aren't. (when he ends up actually seeing Matt's soul mark while patching up his wounds, or something)

Frank hates the idea of soulmates in general (he and Maria weren't soulmates, and in his mind that only meant that their love was more real than the unconditional 'love' at first sight that soulmates feel)

+++Maria and the kids were killed by her actual soulmate, who faced no charges because apparently, no one is expected to act rationally when denied by their mate