Sometimes I tell my husband 'I love you' and he responds with 'Thanks!'. He's got this thing about being completely honest. I once asked him if he missed me while I was away, prefacing question with 'I missed you...', and his response was a blunt 'Not really, I was busy'. The same man, nearly cried when he lost his wedding ring, and nearly strangles me with cuddles at night.
Engineers are renowned for being a socially inept subculture. Unless you are being completely delusional, it really sounds like you have nothing to worry about. Chances are though, that he'll say it, but less often than you, for always and ever. So don't let it bother you, and then get used to that.
“Love is the ultimate outlaw. It just won't adhere to any rules. The most any of us can do is to sign on as its accomplice. Instead of vowing to honor and obey, maybe we should swear to aid and abet. That would mean that security is out of the question. The words "make" and "stay" become inappropriate. My love for you has no strings attached. I love you for free.”
― Tom Robbins, Still Life with Woodpecker