Why do I worry so much about my husband leaving me? He assures me he loves me.

You may want to consider that the worry, by itself, does nothing useful for you. In fact, it may be detrimental to the relationship as the worrying will no doubt manifest itself in some negative way and therefore (paradoxically perhaps) he may well be more inclined to leave should the worry continue. Worry is an apprehension of something occurring in the future. One possible way to deal with the worry might be to say to yourself "no amount of worrying is going to make him stay if he wants to go so perhaps I should just park that thought and get on with keeping the relationship alive".

Past experiences can play a huge part in current relationships. Sometimes insecurities over yourself or where you are on your journey through life can impact this as well. Try to focus on the present moment and feel the love he's radiating towards you.

I imagine because of lack of self confidence. If you don't believe in your worth you won't believe someone sees it. Smile to yourself. You are more than you think dear, don't be afraid.

Sometimes it is hard for us to grasp that someone can love us so deeply. Even though they assure us, sometimes we need even more assurance. Trusting the fact that he loves you, and is not leaving takes time, and for you to open up a bit more to him.