Welcome to the forum! You are in the right place where you will get lots of support and understanding from people who have been where you are and those with a wealth of experience living the poly life.
The beginning is tough, Im the mono in our very new poly journey. I can imagine how not keeping to agreements can shake you up inside. Your partner not calling when he promised is definitely not a good start. The 'live' sex with stranger is uhm..TABOO, selfish and irresponsible!! Safety is the number 1 rule. My husband and I are trying this now for 5 weeks (super newbies), and we are still figuring things out(Sometimes the rollercoaster of emotions gets too much and you want to bolt...but somehow you keep on.) The safety rule is the one thing thats sorted and we are sure of so far. I hope your partner starts taking this seriously because its your lives at stake here.
Good luck, and post often.