Wow, popular thread. Everyone wants to get in on this one
As ApplePi said, it's hard to generalize. And there actually is often a significant difference between different individuals of the same type, which does make it hard. But perhaps INTPf will give you some clues. Here's my two cents.
There is a BIG difference between being interested in someone and being in love. From my perspective the falling love process takes place only
in a relationship. It is possible to love someone, but not to fall in love with someone without the interaction that can happen only in a relationship. So I find it hard to believe you love him as you have described. Now this is not to say you do not, or are wrong, I say that only to give you an idea of an INTP-s perspective of love.
I think we are very wary of love. We do not want to be in a position where we are not in control or feel weak. And yes, we will want to go slowly, and work things out as we go. Everything needs to make sense. You might find that hard to understand, but if you want it to work you will have to try. Do not mention love until you are at the least well into the relationship. And as Bird said, never tell him you want to be with him forever and ever, that's scary, illogical, and very hard to understand.
If you want a lasting, meaningful relationship, you'll have to do it his way, that's just how we work. That means, as everyone has said, slooowwwly. Do not push anything on him, and do not pressure him, the automatic response would be to bail out. It will be hard for you, especially because he likely won't give you much notice as to what's going on. How open are you with each other? Start a conversation about relationships, just make sure you don't bring anything personal into it. Find out his stance, views and thoughts about being in a relationship (in general, not with you, do not
make it personal).
If he does seem open to the idea of a relationship, then you're probably just going to have to ask him if he's interested in a relationship with you. The chances are he won't take the initiative, I can't really see any other way than asking him outright. The key to it would be the way you do it, I suggest the best way would be by being neutral, not bringing emotions or your feelings into it, just asking simply if he would be interested in a relationship with you. And then leaving it up to him, he may need time to think about it.
If he doesn't seem interested in the idea of a relationship, or doesn't want a relationship with you, you'll just have to let it go. Not get emotional about it, not take it personally, not mention it again and not let it affect the way you interact with him. That's the only way you will be able to remain friends.
Ahh.. This all reminds me of the heady days of young love, although I think I'm glad I've been there and got that over with.