OK, the title sounds kinda dangerous, but it's not like that

I volunteer on Thursdays and up until now, have been getting lifts home from mum's husband... except last two weeks he's not been able to do it, so one of my supervisors arranged me a lift with the same guy (who I have only met those two times) who lives near me. I actually got told off for this last week for not having my lift home arranged and definite, and I assured her my usual arrangements would apply this week... except after I got home he dropped the bombshell he can't collect me for the next two weeks... How do I ask this guy if getting a lift home with him might be a permanent arrangement?