English Translation
I was completely in love with him.
completely is not hoffnungslos
well it is, in this particular context 
That is a really difficult one.
“Hoffnungslos” means literally “hopelessly” or “without hope”.
But in this case “hoffnungslos verliebt” means “being love without hope of a cure or an end” and normally not “being in love without hope of success”
So completely, totally, head over heels are okay translations.
I am not sure wether “hopelessly in love” has the same nuanced meaning in English.