Some good advice above.
I'd echo BackPacker's sentiments, and say that if you can only afford to do one, then gliding is the sensible option. If you go for the PPL, have you considered how you're going to fund your flying after you get the ticket?
I'd also second matkey's comment about motorgliding. I have a PPL(A) TMG, which in practical terms is exactly the same as a PPL(A) SEP, with the exceptions that a) you fly in aircraft with a decent glide ratio, and b) it's significantly cheaper to get.
My 2c is to get back into your gliding, and when you've got a bit more $ to spend after you've finished studying, see if you can convert any of your gliding time to a motorgliding PPL. I don't know the rules in Belgium, but I think that gliding time counts towards issue of the UK NPPL with SLMG rating.
Best of luck whatever you decide!
