When I'm talking about Richard (wuzzie), I use "boyfriend", "partner", "SO" and "husband" pretty much interchangeably. I also use "lover" and "primary", but less often. In one sense, the words all mean the same thing to me - what I call someone does not define the relationship - but in another sense, they do all have nuances and shades of meaning.
I use these words as follows:
"boyfriend" to distinguish my male partner from my "girlfriend" and make it clear to people who don't know their names which partner I mean. It doesn't seem quite right for a committed relationship of 5 years+, especially as 26 year old males are not generally called "boys" (I don't have the same problem with using the word "girl" for 26 year old females, as I'm one myself and I happily self-define that way), but I can't be bothered to change it.
"partner" has two meanings for me: when I am talking about the relationship to someone in an official position (bank, phone company etc) when I want to emphasise the long-termness and commitment, or when I want to blur which partner I'm talking about. "Partner" can mean anything: emotional, romantic or sexual relationship, and it's useful as a catch-all word to talk about other people.
"primary" when I am talking to people who understand polyamory terms and it is somehow relevant to the topic of conversation that he is my primary partner i.e. the one I live with/share significant life entanglements with. I expect a primary relationship to be strongly emotional and probably romantic: the sexual parts are optional. You can, of course, have more than one primary: just I don't (currently).
"SO" or "significant other". This is the polyamorist/feminist version of "other half", which is a phrase that entirely nauseates me. Hello, I'm a whole person by myself, thankyouverymuch! SO implies some sort of permanence, that the person you're talking about has been around for a while and will continue to be, without implying that there is only one person who will fill that space at a time, or that I would be somehow lacking without him.
husband" I use almost in jest, when we're talking amongst ourselves. It frequently gets modified with "wuzzie" (i.e. "wuzzie husband") as a term of endearment for Richard, but not in public. I use it in places where "primary" and "SO" might not be understood and I want to make our relationship sound official, but never in a context where it could be mistaken for legal marriage.
"lover" to me implies a sexual relationship. It also has implications of a relationship that is less important than another: someone you rub bits with but don't share housing or money with. This is why I hardly ever use it for Richard.
I do not use "spouse" at all, except in the plural when talking about other people's (spice). I'm sure there's another term that people use a lot, but I've forgotten it now. Bah.
Extra disclaimer that these definitions are just how I use these words: other people's language may vary, I'm just talking about me, etc. I really couldn't be bothered to go back and add "for me" in every single sentence above - just take it as read that I'm not trying to generalise!