Thumb sucking on my boyfriend?

So basically my bf and I have been together for a year now. Sometimes before I would kiss his hands a lot but for the past few months I've been sucking on his thumb and sometimes his index finger. Usually we're just getting ready for bed and if he spoons me I always end up with the urge to just sucking on his fingers. It started with when I would drink a bit too much I would suck the little meaty part of his palm but now it's all the time. Idk why I do this. I never sucked my own or anyone else's it's only with him. I feel extremely open and comfortable with him. He sometimes initiates it too. Oh and sometimes he sucks on my nipples for like hours. Is this a weird baby complex we have or is this kind of normal? I've been feeling a little weird lately but I mean I really wouldn't want to stop.

TL;DR I don't know of my bf and I have weird baby issues or if it's kind of normal to suck his thumb all night and him to suck my nipples all night?