So what does he mean by 'healthy relationship'? What relationship(s) does he want to be healthy? Friends? Lovers? Family? What does he expect from each of them?
Only two chapters in and I only see that MC turns down half-succubus' advances because they're childhood friends, yet she seems to be taking the lead in progressing the relationship further? Does he expect the two of them to stay friends forever, or does he want to get serious when the two of them are adults?
Either the MC needs to reflect on what he wants to do and follow through with them, or grow a pair, accept her advances, and take responsibility from there on, because if she's that into him (unless she has ideas of seeing other guys after this, being half of her nature being a succubus that she is, of which I can totally understand and fear) I don't see why they can't tie the knot then and there.