A husband is a butt buddy for someone else, but you just don't know it till you see the divorce papers on the kitchen table when you get home from work.
How very cynical - and funny!
More seriously, to me a boyfriend means a guy I'm serious about, seeing him exclusively, having sex with him, but we haven't taken the partnership or marriage steps yet. Though we may live together.
Partner means we own stuff together, most likely live together. We've made things legal between us with documents as our State may require. It's monogamous (at least for me), or open with rules.
Husband of course means a legal marriage, where permitted. But I choose to call my partner my husband, anyway, as he does with me. Having the marriage license wouldn't change our relationship and how we live together, but it would give us considerably more legal benefits & protections we don't have now.