I am confused when talking about a general idea using "our life" when sometimes I feel like using "our lives". Please tell me the correct answer with appropriate explanation.
These examples illustrate when you would want to use the singular versus plural of life:
In (2), I imply that we have shared a life, hence we jointly have had one life. In (1), I imply the opposite (different lives have to be counted separately). Consequently, the singular is felicitous in (2), but not in (1).
Felicitous does not mean obligatory, though. You can also say:
This is possible because we each have a life and it is possible to spend them together. Personally, I prefer the singular though.
By contrast, you completely change the meaning by using the plural in:
This no longer means “different from each other’s lives”, but implicitly contrasts with someone else’s life (or lives).
Note that 'I' changes to 'We' as does 'my life' which changes to 'our lives'. In other words, you would use 'our lives' when talking in the plural ('We'), and 'my life' in the singular ('I').