When I was saying my wedding vows I knew I was marrying the wrong man.
This looks like an adjective, but it's actually a noun. This word is the same as the kanji meaning: vow (or oath).
This has the same reading as 近い (ちかい). Just think about how when you're making a vow or oath, you become closer to the thing or person you're vowing to. You belong to them, in a way, which is why you become close (近い).