How can I stop worrying?

I seriously need to stop worrying and get stressed over things. It's becoming such a large problem that I feel that I can't enjoy my life. I'm for example so afraid that my relationships will end that I'm destroying them. I'm extremely jealous and scared that my boyfriend will leave me or betray me, and I hate myself for not trusting him. When I get anxious the pain and nausea is horrible and the only thing I can do is wait until my body is out of energy so that I can't be "physically" anxious anymore. I really don't know what to do about this, because even if I know that the fear is irrational I can't think straight in these situations. I would really appreciate any advice on how to try to think and how to stop worrying.