It's 2 parted.
First part "engage"
1) Target the player that you want to make a couple with
2) Write in chatwindow .engage nameofyourpartner then enter
3) if player has you on friendlist popup will apppear with engage request
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ok cancel
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and a systemsg that you wanna engage with him/her
if not in your friendlist nothing will happen. (/friendinvite nameplayer)
4) if player accepts you are engaged. Congratulations!
Second part "marriage"
1) if you are engaged go to a Wedding Priest named Andromeda
in Hot Springs Guild House (Goddard) and ask for marriage
[ you need Formal Wear (C4Items) and it costs 11k ]
2) your partner goes to the npc and confirms after you make the request
3) fireworks,wedding marchs and your are married
You can use .gotolove nameofyourpartner to teleport to your partner if
you're married (costs 500 adena)
if you want to cancel your engagement / marriage enter .divorce nameofyourpartner
if you're married you have to pay 20 % of adena to your partner
When you try to engage with someone and you have already a partner you get
a bighead + debuff
You find a priest NPC in Hot Springs Guild House (Goddard).