If you cannot reach your co-founder by call, he should not be your co-founder. I have made the experience that people who once prove that they are unreliable, remain unreliable. I also made the experience that people who you really believe are your friends, may see you as a riding horse or tool. When the time comes that you realize that by getting fooled heartlessly, this will shock you, because loosing trust in a friend is one of the most shocking experiences in live. When you've read this far, you should definitely NOT hesitate and do an overly early reaction, my experience is also that things often change the complete meaning, when you don't share positions and feelings. I'm fair but hard, you can be whatever you want, but do not be naive or a tool. Stay smart and sweet-tempered =)