When should you say I love you to your boyfriend?

Most guys will want to be the first to say it (just like they want to be the first to kiss you), so sometimes it's best to wait. However if you don't want to wait, you can encourage him to say it by asking things like "Do you think we'll stay together for a long time... maybe all of our lives?" and such, but not a direct "Do you love me?". You could tell him you want to stay with him forever; like that most guys won't feel like you took saying "I love you" first from them.