Can you marry in Belgium as a non-Belgian couple of the same sex?

Yes.

In Belgium the marriage between two people of the same sex is possible if one of the future spouses is Belgian or if they have their regular abode in Belgium since 3 months.

Therefore one of the future spouses must be either

* Belgian

* or have their official abode (the place where for instance your mail arrives) in Belgium

* or must have their regular residence in Belgium for more than three months