Most Helpful Guy
Another possibility is he knows things aren't well and he senses you want to leave so this is more a manipulation tactict to get you to stay. Don't go on that trip ask your mother if you can stay with her and get out asap
Most Helpful Girl
It does sound like a catch-22. That if you go on the trip, you'll lead him on and he may propose. If you don't, you'll lose money and upset him by foiling potential plans to propose.
Ultimately, I think it's best to bail out. Money can be earned back. Just imagine how much shame in combination with heartbreak he'll feel if he not only gets broken up with you, but much less after he gets his proposal rejected. Calling things off, or at least voicing how you've been feeling as of late, would be the better option. Quick and (relatively) painless.