Learn French: Ils vont se marier par amour. - They are going to marry for love.

To say what is 'going to' happen, you use the present tense of aller (to go) followed by an infinitive verb (the unconjugated dictionary form). Here, we have Ils vont (They are going) plus the infinitive se marier (to get married).

Why is it se marier and not just marier?

In French, the everyday verb for 'to get married' is the reflexive verb se marier. You can think of it as meaning 'to marry each other'. If you use marier without the se, it means to officiate a wedding, which is what a mayor or priest does!

Does the reflexive pronoun (se) always go right before the infinitive?

Yes! In the near future structure (aller + infinitive), reflexive pronouns like se must go directly in front of the infinitive verb they belong to, not in front of aller. This is why it is Ils vont se marier, and never Ils se vont marier.

Why do we use par instead of pour for 'for love'?

While pour is the usual word for 'for', French uses the preposition par to express the emotion or motivation behind an action. So par amour translates to 'out of love' or 'for love'. You will also see this in phrases like par curiosité (out of curiosity).