I think you need to ask yourself what it is that's making your BF hesitant to committing to moving your relationship along. I think you also have to ask yourself why you aren't spending more time together.
My DH and I didn't live together before we got married but we spent every weekend together. We didn't have to do anything special, we just wanted to be together. Sometimes we'd just lay on the couch reading the paper or go for a walk. Nothing special, just time together.
I wouldn't bring another person into the relationship until you get a clear understanding from your BF as to where things are going. Also, getting involved with someone else in an effort to make your BF jealous and prehaps propose is a recipe for disaster.
I hope things work out for the best.