How can a husband forever stay happy with his wife?
Honestly, a husband can't stay happy with her wife forever. Its totally hypothetical. There may be a lot of good days and very few bad ones but there will be a balance between happiness and sadness.
You can keep the love intact between the two of you and treasure it all along and build on it. This will keep you two happy, most of the time. don't forget why you love him and don't let him forget why he loves you. Tell each other everyday that you love the other person, because sometimes the most obvious things need to be said to keep a relationship in check.
This is pretty much everything that I can suggest to you.