This might be rough to hear, but one reason he stopped saying it could be because that's not how he feels anymore.
Guys are notoriously non-confrontational when it comes to women in our lives.
Sidenote: I recognize that's not a universal truth, but more times than not, we just want peace.
And we do not like hurting feelings of women we are tied to. Nobody wants to be the bad guy if they can help it. So in the most bassackwards attempt at chilvalry, we'll just avoid the situation with gusto and hope that it fades out on its own. Or that you'll leave. Which is stupid because we still caused the departure. Man logic is definitely as flawed as chick logic.
I think what you need to do is talk to your man and ask him where his head is at. If you ask him if he loves you, outright, he'll probably say "yes" very quickly. Tell him to slow down and really think about that because you're noticing a difference and you want to know if there's a problem, what it is, and if it can be fixed. Pretending to be there is going to do more damage than he thinks.
Part of the reason why I think that's the reason is because men use the word "love" in a very cavalier fashion a lot of times to get what we want out of women. So a man who stops using it probably means that he did in fact mean it...and now he's not sure.
Again, man logic can suck as much as chick logic.