My boyfriend has started belching almost comstantly. He says he is afraid if he doesn't the air he has swallowed will travel to other parts of his body, such as his heart or chest cavity. It's starting to interfear with everyday tasks and keeping him up at night. How can I reasure him that this is not possible and any air that may be in his stomach will not hurt him?

Tell him to stop being an idiot as his constant passing wind in this manner is becoming seriously annoying.
His "concerns" are completely unfounded and I think he's using it as an excuse to be gross and childish around you..

If he believes that this really is a problem then he needs to see his own medical practitioner as soon as possible..