A couple working through this issue together seems to need (at a minimum) to resolve the following questions in order to make a clear decision on cohabitation:

All moral questions should start at the level of, well, morality.  Thus…

• Do we believe it is morally right to cohabitate without the vows of marriage being taken?  Why?  Why not?

If it is morally acceptable, then is it wise?  Which leads to such questions as:

• Will this enhance our relationship, and if so in what specific ways?  How are these superior to marriage?
• Do we intend to be married in the future, and if not, then why live together now?  If so, why cohabitation over marriage now?
• How will this affect our finances and property?  What will become “shared” property, and will anything be kept separate from the situation?

Finally, it is always wise in matters of at least partial emotional concern to seek the wise counsel of others, so…

• What do our friends think of this choice, or have we even discussed it with them?
• What do our parents think of this choice?
• Are there wise people who have already made this choice, and have we sought their advice?  How did it work for them?

If nothing else is obvious from this experience, it should be that decisions such as living with someone are life altering decisions and should be made carefully and slowly.  Think through all sides of this issue, not just the one that supports your desire, and then choose wisely.