Sheesh, some of you people have spent way too much time living in real life!
So much cynicism and fear. This is a vanilla shoujo manga; their odd little psychological quirks are just there to add a little spice to the proceedings. There shall be no yandere or replacements with other people; there may be a love rival or two at some point, but they will be inconsequential.
If anything, his earnest in-the-deep-end approach to love seems to be just what's needed to open her up to the idea of heightened feelings and specialness to someone. It helps that for someone so over the top, he's admirably patient. Although, I'd say he can be patient just because she's not judgemental--she may not share his feelings but she never invalidates them 'cause she's a generous spirited sweetie.