partner running out of time !!

My partner and I met earlier this year and were friends for a while. We haven’t been together long due to religious reasons but became engaged last month. His visa runs out in 3 weeks as a graduate, he wants to do a masters but that hasn’t been accepted yet and wouldn’t start until september. I stay with him permanently but am not on the tenancy so we don’t officially live together. I’m freaking out a lot and have no idea what we’re supposed to do, how does this all work ?