For a three-act plot analysis, put on your screenwriter’s hat. Moviemakers know the formula well: at the end of Act One, the main character is drawn in completely to a conflict. During Act Two, she is farthest away from her goals. At the end of Act Three, the story is resolved.
Act I
Connie's youthful dreams of a happy marriage and meaningful life have come to die at Wragby, where she's committed herself forever to a bad-tempered snot of a husband, who also happens to be paralyzed from the waist down. Plus, Wragby has a really insubordinate gamekeeper, and he and Connie dislike each other right away. Obviously, they're going to have sex.
Act II
Connie finally has sex with Mellors, and it's way better than any sex you've ever had or ever will have. So good, in fact, that now she can't stand being around Clifford. She and Mellors make a kind-of-plan to run away together, and then she does what rich people always do when they have a problem: takes a vacay.
Act III
While she's away, the whole story emerges. Connie, with a questionable sense of self-preservation, spills everything to her sister and father, and Mellors's soon-to-be-ex-wife spreads the gossip around Tevershall. But Clifford, like the spiteful guy he is, refuses to give Connie a divorce. At the end of the book, nothing is resolved—except that D. H. Lawrence has a pretty dim view of human nature.