My INFJ bf just outright told me that he couldn't tell how I feel & needed me to express it more. It made me aware that I needed to lower my guard a bit if I am going to have a successful relationship, and that just because I feel something strongly doesn't make it obvious to others. Fi-dom turn feelings & emotions inward, and especially will they bask in a positive feeling internally, forgetting to communicate it. Don't prod or push him to express his feelings(or guilt-trip or cling), as that can backfire, but do let him know that you'd like him to be more expressive so you know where you two stand. Then drop it & give him time & a chance to meet your request.
As for being slow-moving, INFPs can also mentally view the relationship as moving to another level, but again, forget to communicate that. This is because these intangible dynamics are very "visible" to us (and I'm sure ENFPs relate to that), almost as obvious as physical object in front of your face (if not more so at times). I saw my INFJ as my exclusive boyfriend after about 2 months of dating, and when I off-handedly referred to myself as his girlfriend one day, he was pleasantly surprised. I sort of took it for granted that it was obvious we were exclusive, but he needed to hear it from me & make it "official". I admit that I kind of have an "if I didn't love/like you, then I wouldn't be with you" attitude at times, and so I have to make a conscious effort to give verbal affirmation. So you might test the water at times with your INFP & be surprised to find out it's warmer than you imagined, and you can do that without seeming needy or pushy. It's not like the only two options are "suffer in silence" or "dramatically declare intense feelings".
If you're an INFP also, then you might not be aware that your own feelings are not as obvious as you suppose either, so make sure to communicate what you are feeling too.