I don't like and don't watch the anime, for a variety of reasons, but
I _do_ know the Secret Sauce story is still in it.  And that means
that this general sequence of events still came about:

-Ranma promised Ukyou TWICE to marry her, of his own free will.  Once
when they were children, once when adults.  The child time he didn't
quite know what he was promising, but the second time he DID.

-Ranma did this because he did not want to make a choice between Akane
and Ukyou (they had previously tried to force him to choose); Ranma
decided the preferably alternative was...well, let me give it to you
in fem-boy's own words:

Ranma: I'll make Ucchan dump me!  I will get dumped!
(Flashback: Ranma promises to take care of Ukyou forever, who is
ecstatic, saying "Really, Ranchan?")

Ranma: Then all I have to do is treat her like dirt!
(Scene shows a mental vision of a drunken Ranma kicking Ukyou; the
vision then switches to Ukyou, crying, running out of the Tendo's
saying "I can't take it anymore!"; back in the real world, Ranma
smirks.)

Ranma: It's a perfect plan!

And, I might add, he tried to implement this plan.  First, he tried to
do so by throwing away her cooking and calling it 'slop'; foiled by
the quick reflexes of everyone else at the Tendo table.  He also bought
booze, dumped it over himself, and tried to feign drunkeness as he came
home and beat up Ukyou; this didn't work because she gave her
patented cure for drunkeness by splashing him with ice water.  Third,
he tried to put lipstick on his clothes, but Ukyou caught him (in
female form) in the process of doing so.  Finally, he went to spend
the night in Akane's room, calling her his lover.  This almost worked,
except that Ukyou eavesdropped and got the impression (due to what
was said and what had happened earlier, a quite reasonable one) that
Akane was forcing Ranma to do all these things.  Ranma's next plan
was to treat her like Akane (in other words, insult her), but this
was cut short because Ukyou, in an attempt to prove her devotion, had
drank some of the horrible okonomiyaki sauce that was the root of the
mess and gotten sick.

Thus, because Ranma had been afraid of telling the truth (he had
ruined the sauce ten years ago), he was caught in a web of lies,
and finally he decided that the 'best' way out was to promise to
marry Ukyou, and then try to drive her away by hurting her where
she was weakest: he tried to insult her cooking, the most important
thing in the world to her; he tried to physically abuse her, and
he tried to pretend he was unfaithful to her.  What excuse can you
give for this?  What possible justification?  And what's more...did
it even work?  No.  Through all of that, Ukyou didn't even waver
in her devotion to him.  Why did she leave?  She left because she
had vowed to herself that she would give up okonomiyaki for Ranma,
and when she reflexively tried to cook it later, SHE decided she
wasn't ready for Ranma and left OF HER OWN FREE WILL.  She didn't have
to.  She HAD Ranma, she had him and there was nothing anyone could
truly do about it, because he had given his promise (and there were
witnesses, yet).  If Ranma didn't inspire such total, selfless
devotion from her...well, they WOULD be married.  Ranma was even
getting closer to her by the end of the story... <shrug>  Maybe,
would be, should be, all irrelevent.  The point is, there's no excuse
for what Ranma did in that story.  NONE.

Despite all that you have said, Ranma still does show some of his finer
points in that story and that he does care for Ukyo to some extent.  To
prevent anything from happening between him and Ukyo, Ranma slept in tree
the whole night.  Though, Ukyo might not have had any of THAT sort of thing
on her mind, she is affectionate.  I wouldn't put it past her to cuddle up
with Ranma during the night.  To prevent Ukyo from drinking any more of the
sauce that she thought she had made, Ranma drank it all within one gulp.  He
did not want Ukyo to be hurt anymore.

Besides, I think this story arc proves Ranma cares for Ukyo as much as he
does Akane, if not more.

Fact 1
He cared more about whether or not he stayed the night with Ukyo that Akane.
Ranma is shown to be very shy about intimacy.  This shows that he was not
even thinking about doing THAT with Akane even though there was so much much
talk going on about having a mistress.  The connection between a lover and
Akane did not even register.  With Ukyo, he took one look at her in his bed
and decided that it was safer to sleep in the tree.  I do not think of Ukyo
as a slut so I think that she really wanted to sleep with him as if they
were just five years old and relive old times.

Fact 2
Ranma is depicted as a lover of good food.  Many stories show this,
including the fortune telling food episode.  He ran away from Akane's
fortune telling food at first, despite the fact that he could find out once
and for all if Akane was the one for him.  At the end of that story a happy
Akane is seen feeding Ranma after she finds out that Ranma may the one for
her after all.  Ranma was willing tell the truth about the 'petals' on his
face and go back to the old angry Akane rather than continuing eating her
food.  In the secret sauce story, Ranma sees how much pain Ukyo is having
and decided to end it by drinking all of her sauce.  He has tasted this
sauce before and knows that it is very horrible in taste.  By the time he
drinks all of the sauce he has already told her of his actions ten years
ago.  So he is no longer hiding anything from her.  By drinking this sauce,
it shows that he really did care.

P.S.  On a totally diffent note, when are the rest of your stories coming
out.  Waiting for rest of Kyoto Chronicles, Affairs of the Heart, and Curse
of Darkness.