Love and attraction idioms: verliefd worden op (to fall in love with — literally to become in-love on), smoorverliefd zijn (to be head over heels in love — smoordrunken with love), het hoofd op hol brengen (to make someone’s head spin — said of someone who makes another dizzy with attraction), iemand het hof maken (to court someone — old-fashioned but still used), iemand versieren (to chat up/seduce someone — informal), aanknoopjes zoeken met (to seek contact points with — to try to start a conversation with someone you are interested in).
Relationship and marriage idioms: met iemand optrekken (to spend time with someone — to hang out), goed bij elkaar passen (to suit each other well — to be well matched), hand en span vormen (to form a close team — said of a couple who work perfectly together), voor het altaar staan (to stand at the altar — to be on the verge of getting married), samenwonen (to live together — very common in the Netherlands before or instead of marriage), trouwen op het stadhuis (to get married at the city hall — the civil ceremony).
Heartbreak and friendship: het uitmaken (to break up — to end a relationship), gebroken hart (broken heart — same image as English), beter een goede buur dan een verre vriend (better a good neighbour than a distant friend — prioritise those nearby and reliable), vrienden voor het leven (friends for life). Dutch people tend to have a small number of close vrienden (friends) and a larger circle of kennissen (acquaintances) — the distinction is important and the word vriend carries more weight than the English friend.