Drywall mount

Does the beam seem to be metal, or wood? If wood, it's exactly the right thing to mount to.

Adhesives are a terrible idea for your situation. Go stick a drill bit into the hole you already drilled and use it to measure the depth of the hole to the point where the bit touches the beam. Come back and tell us that measurement.

the beam is metal, it's a modern complex. i stuck the bit in and got

In that case, you're dealing with something other than drywall. No drywall is 1-2mm thick. Maybe it's just a plaster skim coat. You may need to come up with a way to mount your curtains to the wall. Again, adhesives are not the way.

Thank you for your replies, greatly appreciated. There is a possibility it's concrete. can i drill into that?

Yes. There are special anchors (inserts) you can use in concrete. To find out what you've got, you can ask the landlord or maintenance people. Or, pick up a titanium drill bit, take a brief shot at the material, and see what sort of debris or dust you find on the drill bit. You'll need to remove enough of the surface coating so its dust doesn't obscure the evidence gotten from the beam.

Or, mount the curtains on the wall.

Either way, I'd suggest that you open your phone book and locate a good hardware store. Not Home Depot. Not Lowes. Not Wal Mart. A real hardware store. We can tell you the names of hardware to buy, but when you get them home, you will still be clueless. You need to speak to someone standing right in front of you.

Or maybe he hit a strip of metal corner bead.

Now, that's an interesting possibility. A very small drill bit and a test hole further from the edge would verify this.

Or simply drilling the existing hole a little bit deeper.

Explosives. It's time for explosives.