Is love something you say, or something you show?
Be satisfied with the love he wants to show... a hug, a moment he wants to spend with you, times where he wants to share something special with you.
My son is eight. Sometimes, when I say "I love you", he will reply with "I love you, too." Then there are times where I say that and he's in his head, thinking about something more pressing to him. He's reassured and aware of our love for him so it's not something he pays much attention to. Sometimes I get little notes from him, sometimes it's an origami heart or sometimes it's him wanting me to snuggle him in his bed while he's waking up. We chatter and laugh and are silly.
Love is in the actions, not the words. Saying "I love you" is one thing, living it is another, entirely.