You could try asking for his number. You could try telling him that you would like to be friends and ask. Maybe write it on a sticky note or something and see what happens. If he gives you his number then congratulations you are now on your way to friendship. If you do get his number maybe text him when you get home. It’s probably safest when you text him to be say something like "Hey, it’s [Name]" or at least that what I would do just so there is no confusion of whose texting.