Ok here's my story.
I told my DP I loved him after a few months together (back in the mists of time), and he went all silent and funny. I instantly regretted it, and within a few weeks we split up as I realised we just didn't feel the same way about each other.
Two weeks after that he begged to have me back, and said he was sorry he just hadn't realised how he felt about me, but that being without me made him sure how he felt. After much discussion, we got back together.
It was great to be back together but it took him a further two weeks to say he loved me (the actual words), and he said it as he kissed me goodbye in the morning and I was still half asleep. We've been together 10 years now and he says it every day.
I don't know what the moral is - maybe that if you say it and he doesn't immediately say it back (which he may well not do, for any number of reasons), don't assume it's a write-off.
Some guys really struggle to say those words out loud, but once they've 'broken the seal' they can be as vocal and loving as anybody.
Anyway, your feelings shouldn't be a dirty secret. You can tell him how you feel, it's allowed!