When we married way back in 1964, we saw it as a statement of our love, togetherness, having children (two) & to live happlly ever after. Fortunately, we've managed to do all of those - so far!
However, times have changed & like your boyfirend, lots of people can't see the point in marriage, for whatever reason.
My own personal, albeit old fashioned view, is that if you are thinking of taking on the responsibilty of having children, I think it's nice to have the commitment of marriage too.
Having said that, if anything were to happen to my husband, I wouldn't want to get married again, after all, I'm too old to have any more children & that would be the only reason for me wanting to re-marry.
Besides I don't think anyone could fill my husband's shoes!