How do you know?

How do you know when your relationship is getting serious? Like my boyfriend and I are trying to be more financially stable before we make any huge decisions is that bad? Even though we've been together for awhile, 2015, yet known each other since 2011. He wanted to go for a full blown relationship in 2015, instead of being friends. We're both working 2 jobs, 2 separate households, we don't live together yet, we're both looking for a house though. We just hadn't had that marriage talk yet because we want to be financially able, but not rush. We're both ok with that. I only asked because my guy friend asked, he's currently engaged, as of yesterday. I told him CONGRATS!!! But how do you know it's that serious or if it isn't?