Confront the promise-breaker for real. This is the time for assertive behavior and constructive criticism. Avoid blame, avoid saying "you" statements. (See How to Practice Nonviolent Communication.) Stick with how their broken promises make you feel, and why you see their promises as being both "broken", and as "promises" (hence the reasons why you did the exercises above). Tell the promise-breaker:
How this has made you feel
How this has impacted your personal/professional life (give concrete examples)
Why it is that you feel you can no longer place the same level of trust in your relationship with them (give examples of the key time or series of times they have proven incapable of maintaining the promise)
How you still care about them as a person but that it is time to let them know you will no longer be asking for their word, as you simply cannot rely on it (this ties in with the next step on forgiveness; you are not rupturing the relationship, just ordering it clearly).