I have no doubt you will soon learn to "get" Shakespeare. It is mostly a matter of practice, of reading him enough to get used to the grammatical inversions and odd vocabulary. A lot of it is just getting used to reading poetry,which is what all of Shakespeare, including his plays, actually is. You are certainly intelligent enough to be able to master this.
If you want to use wedding vows, get a copy and cite them, quoting normally. This might cause a problem, though, if you are not allowed to use outside sources.
Some hints to guide you in your thinking about the sonnet:
Shakespeare sees love as being until the "edge of Doom"--the equivalent of 'til death do us part.
Yes, but love, at least within marriage, is much worse than that. It's through all the alterations of old age. So, for such love to last, it must be the case that "Love's not Time's fool, though rosy lips and cheeks / Within his bending sickle's compass come: / Love alters not with his brief hours and weeks, /But bears it out even to the edge of doom."
"If this be error and upon me proved, / I never writ, nor no man ever loved." = If I am wrong, and this is ever proved by own inconstancy in love, then I have never written anything and no one has ever really loved. In other words, This is not an error and I will never be inconstant in love.