how do i ask my mom if i can stay the night at my boyfriends house?

i’m 19 (20 in a few months) and my bf is 21. we’ve been together for 2 1/2 years, known him for almost 4 and he lives on his own. i’m really tired of making the drive back and forth every day. it uses so much gas and i drive home late and exhausted which is dangerous and not great for my sleep schedule. i didn’t have a problem with this when i lived less than 2 miles from him, but now its 30 miles. my mom knows him very well, and likes him. he has been on multiple vacations with us and hes spent plenty of time with my family.

i don’t necessarily want to stay the night every night, just maybe like 2 nights a week to save time and gas. the problem is my mom is very religious. for some reason she thinks sleeping in the same vicinity as a man leads to sex (i’m at his house alone with him every day, not sure why shes still worried about that lol)? she thinks its wrong to do before marriage. you get the gist. i’d say i’m pretty responsible for my age. my main priority is school, ive never drank, done drugs, gone to a party, etc. i’m really not trying to cause any problems.

also, i would really appreciate advice other than “you’re an adult just do whatever.” i think thats disrespectful especially since i still live under her roof and i’m not financially independent. just because i am legally an adult doesn’t actually make me an adult. i really don’t want to disappoint her or make her think i’m being problematic. if i’m being unreasonable by wanting to spend the night at my boyfriends just be honest with me please.

sorry this is so lengthy i wanted to give context.

TDLR: how do i (19f), ask my mom if i can stay the night at my boyfriend of 2 1/2 years house (21m) in a respectful way?