Guy friend issues, please help?

i have a guy friend who ive gotten kinda close to. He's recently said that he loves me, he wishes he could be mine, and whatnot. I've been with my boyfriend for 2 years and we are engaged; my guy friend knows there is no way anything can or will happen, and ive made that very very clear to him. He says he understands and that we are on the same page. We have still kept our friendship, but its very difficult at times because I like to be open with my friends, but even saying "love ya, and putting a heart like I usually do with my friends, makes me nervous with him. And now every time I'm not on facebook for a few hrs he comes on and says "you're so different" then leaves. If I'm online and I don't respond quickly enough, he gets upset and leaves. I can't do anything without him getting upset it seems and it aggravates the crap out of me. I've already tried to explain to him to not do that, or think that way when im not online, but it doesn't seem to be getting through to him. I've thought about somehow not talking to him, but he's already told me that I'm the only thing in life that makes him happy. I'm really confused on what to do. I just dont know how to handle this situation.