When should I tell him I love him
we've been off and on for a year and were dating again!
You should tell her immediately since you are not new to each other. This will help you know what he feels about you before it is too late. Look for a perfect time when you are just the two of you and say it.
When you do actually love him. Only tell him if you actually mean it.and just generally in life, don't ever say something if you don't mean it.