Other things you could say include ‘you are my one in six billion’, ‘if I couldn't spend my life with you, I would jump off a cliff’, ‘every second with you feels like I’m in heaven’, ‘without you all I am is incomplete’, ‘I miss you already darling’ or sweety or whatever nickname you call him.
There are also other ones such as ‘I love you to the moon and back’, ‘I love you more than words can say’, ‘you complete me’, ‘you mean so much to me darling/honey’, ‘all I want to do is make you happy’, ‘I love you more than anything in the world’, ‘seeing you lights up my world’, ‘seeing you always puts a smile on my face’ and even ‘I could not bear to be without you’.
Above all you really just need to be yourself. Describe his looks, so if for example he has dark hair that is all nice and shiny compliment him or if he has nice eyes say so. You should simply mention how he looks, what you like about him and how he makes you feel. Make sure you are poetic and don’t be scared to be a bit metaphorical, like ‘to me you are the final piece in my jigsaw piece, without you, I wouldn't be complete’.