Two quotations to help you:

“Feel the fear and do it anyway.” – Susan Jeffers

“Pay the price. Don’t be so afraid of sudden, sharp discomfort that you willingly tolerate chronic, continual, deadening pain the rest of your life.” – Harry Browne

And I agree fully with Kelly that you’re not doing your current partner any favours by staying with him out of obligation or guilt, and that you will be kinder to him to set him free to be available to someone who really wants to be with him.