There's no exact right time because every couple is different, but 3 years is already plenty of time to know each other well and figure out if living together makes sense. What matters is that you're both ready, not just that a certain amount of time has passed - so instead of focusing on whether you need more or less time, ask yourself if you've already worked through those doubts about living with someone. One way to test it is to spend several days in a row at your partner's place and see how it feels, or have a real conversation about how you both imagine daily life together (chores, money, personal space). If you're still scared after that, it's okay to tell your partner you need more time; if you realize it's more fear of the unknown than real doubts about the relationship, it's probably worth trying.