It is really hard to say that all 3rd-party involvers are bad. Marriage is too complicated, and believe it or not, it is hard to make a perfect match the first time. I have seen too many examples that a grand opening of a marriage dies slowly with various internal/external factors.
Only the person who wears the shoes can tell whether the shoes fit his/her feet well. If I could dare to say that marriage is also like an investment or shopping, when you find your investment is wrong, what can you do? I think looking elsewhere to re-investment is a normal behavior. Of course, this re-investment can be called "betrayal" to the original "company", and the investor can be blamed for not being cautious enough at first time when making the inital investment, but this kind of investment mistakes DO HAPPEN, otherwise, the world is perfect, and there will be no tears / laughters at all.