Marriage in Henry Fielding's The History of Tom Jones, A Foundling, is a rather convoluted affair (no pun intended, although there were more affairs in marriage than there was fidelity in marriage). Marriages were undertaken (no funereal pun intended there, either) in Tom Jones for a variety of reasons. Marriages were undertaken for necessity, as in Bridgett's baby being born eight months after her marriage to Blifel, and, yes, the customary time of pregnancy is nine months, which is particularly interesting because Bridgett met Blifil one month before the marriage.
Marriages were also undertaken for money, as was the case when Mrs. Arabella Hunt proposed to Tom and he was tempted, though he finally declined. Marriages were sometimes undertaken for love and necessity together as when Nightingale and Nancy were married. This brings up the point that marriages very often went against parents' wishes and that parents' wishes were not always honorable ones as in the insistence of Western insisting that Sophia marry young Blifel even though she plainly detested him and he only consented to aggrieve Tom.
Marriages were sometimes not undertaken because they were deemed to be odious. A woman of beauty and independent means, with her pick of paramours, might very well loath the thought of marriage and attempt to do away with suitors as was the case with Lady Bellaston who refused Tom's mock proposal (no sincerity in that one at all) and attempted to have him shanghaied into the navy (which means conscription would have been decidedly against his will and without his choice). Additionally, marriage was unfavorably viewed by virtuous young women who knew that a suitor had too much "experience" with liaisons, as was the case in Sophia's eventual reaction to Toms' "experience" (of which he had waaay too much).
Finally, in the end, in Tom Jones, there were marriages that seemed to be respectful and loving but really had secret undercurrents as in the case of the Fitzpatricks, as he was found to have a mistress in the person of Mrs. Waters aka Jenny Jones. And then there was Tom's eventual marriage to Sophia ("sophia" is the Greek word for "wisdom;" mull that one over), which was founded on every human flaw and foible that Tom could manage to muster up, although all overlayed a good heart that sought what was humanly just and decently honoring of human dignity--unless the human was the periodic woman well versed in seduction. It appears from Henry Fielding's narrator's comments that Tom and Sophia's marriage was the real thing between two people tested in the forge and found to be (believe it in Tom's case or not) virtuous.