how do you get over those things that you have lost opportunities of jobs and relationships

how do you get over those things that you have lost opportunities of jobs and relationships I find it very difficult to order drinks or food when I'm in a restaurant or a coffee shop, even with friends that i know for long ago, even more worse if i would been out with a new person, the job I wanted i was rejected in the interview because I couldn't say a word and i was completely calm, I wanted to know if someone is in place like me how do u dealing about losing opportunities or relationships from the difficulty of speaking?