I agree that "Dating" is the "getting to know you stage." ...you see a cute person at a mall/restaurant/bar/party, etc. and decide to exchange numbers; and then later decide to text, or call this person in order to set up a time/date to hang out with JUST that other person...this could possibly include sex, depending on what feels right for those two individuals (and what's in their comfort zone).
If all goes well on this and several other dates; numerous follow-up texts, and/or phone calls; and these two cannot stop thinking about one another (and, hopefully, in more ways than one)...then they can talk about seeing each other more exclusively... this is what I would consider becoming "boyfriends."
Sometimes, boyfriends can and will also decide to move in with each other (and will NOT call/consider themselves "partners"), and at this stage, they might start uttering the "three word phrase" that many of us long to hear. Love will be new for them in their relationship, and when this love grows -- significantly -- they may decide to get a partnership with that current boyfriend.
IMO, boyfriends cannot progress to the "partner" stage unless they have a signed "domestic partnership" for, at the very least, their city; their state; or even further, a marriage that is allowed by their state or province, etc. (or at least would consider doing so). A partnership also involves a lot more common-law interests... shared properties, bank accounts, vehicles, credit cards, expenses, debts, etc.. A lot of partnerships also involve a longer length of time knowing and caring for one another; and more than likely, they'll have a rich, memory-filled history (good and bad) that further links them to one another. COMMITMENT is a key, here. One looks out less for themselves in a partnership, and looks at things with more of a "What's good for the two of us as a couple" type of mentality. They would, in a partnership, consider moving out of state with the other - if a job were to move one out of their current city, or if there was an educational opportunity that would be great for the other's career, and ultimately, both of their lives in the long run. Talk of children, living trusts, care of an older loved-one (like an elderly parent who may need special care) might be discussed, and provisions made for these new circumstances/decisions. More often than not, things that might end a relationship for two boyfriends, might scar a partnership, but due to their history, and love, will not end the said partnership... a lot more can be said here, but I am getting tired of writing. LOL