Well as long as the two of you are on the same page that this is just platonic love and not anything else, I don't see why not. Not in a serious way of course because that would imply more than just a platonic relationship but I would say a more casual "I love you" like the kinds you would say to friend who's a girl or to your parents or siblings or whatever. Just as long as you don't think of it as a big deal, then you wouldn't act like it is and it wouldn't be all that bad honestly. This type of thing also applies when telling a guy who you only like as a friend that you like him (not in that way) if you ever find yourself in that situation. But if he starts grinning and giving you flirty/romantic cues, quickly recover by adding "you've always been such a good friend" or something like that. Yes, it's like friendzoning him but sometimes it has to be done. That's why I said that it needs to be important that you two are on the same page about your friendship and therefore no one would get hurt.
I have a guy best friend and I tell him I love him all the time even though I've been in a romantic relationship before with someone else and have dated other people. This guy friend and I have been nothing more than just friends so trust me when I say that this isn't something that only friends who might have something more going on would say. "I love you" is honestly something I believe anyone should be able to say to whoever they want in order to show them love, no matter what kind of love it may be and that it's important for everyone to hear it from someone they're close to from time to time. Of course it shouldn't be treated like dirt or else it'll lose it's meaning but it definitely shouldn't be reserved to only a certain type of relationship or gender. Girls say "I love you" to their friends who are girls all the time which is why I think that it's a bit unfair that that isn't socially acceptable for platonic male-female friendships or even platonic male-male friendships.
Anyway enough about that. Point is, if you think that he'll take it well and not in the wrong way, then you can tell him that you love him. Don't be too worried about what other people around you may say although it does help to say it only around people who would also understand your platonic love.
