iMessage message it’s going as an sms and says it can’t be delivered

I’ve been talking to my boyfriend whole day and it’s been going through as imessage ( do blue )

I woke up and sent him a message , now it’s going as an sms but it also says it can’t be delivered ?

i know he didn’t block me because I have him on all other social media.

i did send him a message and for the first time ever , his phone seems to be off as the tick didn’t deliver all the way but it did send.

im very worried as he never goes a day without talking to me

and his phone is never off

could his phone have broken ? So he took his Sim Card out ? Could his phone be off and now it’s not sending through ?

please help me

[Re-Titled by Moderator]