How can I get my baby to sleep through the night?

I have a question, my son is almost 9 months old. He was sleeping through the night pretty consistently, but the last few weeks hes been waking up at night crying, he doesnt want a bottle he just wants to be held. We’ve never co slept. And I’m not sure what to do I dont want to start co-sleeping now and I cant just hold him all night. I take him and rock him then he falls asleep and within me leaving the room hes back up again. I let him cry for a few min hoping hell fall back asleep but no luck. I’m not sure if anyone has any ideas to help him stay asleep. I dont like letting him cry and he wakes up our older son (who’s 3) which isnt fair either.