We first find out exactly how generous Squire Allworthy is when we meet poor Doctor Blifil. Squire Allworthy is a patron, which means that he financially sponsors causes (and people) that he finds worthy. Squire Allworthy's particular focus seems to be educated but poor men who need a helping hand to survive.
One of these is Doctor Blifil, a man of great learning who absolutely hates his day job of being a doctor. Since he despises the only work he can do that could actually make him any money, Doctor Blifil can't afford to feed himself. Squire Allworthy steps in and invites the man over to his house often, so that at least he won't starve.
Now, Doctor Blifil notices that Bridget Allworthy is a wealthy woman, which makes her extremely attractive to him. He's already married (though he and his wife are separated), so he can't personally propose to her. So Doctor Blifil contacts his brother, Captain Blifil, to woo Bridget. (We guess he figures that, if he can't make his own fortune from Bridget's money, at least he can keep it in the family.)
Doctor Blifil's plan backfires. His brother does succeed in eloping with Bridget, partly using Doctor Blifil's advice about Bridget's likes and dislikes. But after Doctor Blifil helps to smooth things over with Squire Allworthy once his brother and Bridget have eloped, Captain Blifil is so ungrateful and annoyed at having benefited from his brother's help that he turns his back on Doctor Blifil. In fact, Captain Blifil is so openly rude to his brother after his marriage that Doctor Blifil finally has to leave Squire Allworthy's estate and move to London, where he dies.
Captain Blifil's treatment of Doctor Blifil tells us a lot about the man Bridget has married: not only is the captain mean and cruel, but he is also deeply jealous. Doctor Blifil is actually wiser than the captain, the captain knows it, and his resentment is part of the reason that he treats his brother so badly when he can't use him any longer.