Informal way of saying "on the contrary"?

Example:

The casual encounters didn't work for me, though. On the contrary, each of them left me emptier than before, made me feel guiltier than before.

The only option I can think of is no. Other suggestions?

Solution 1:

You can use rather:

Used to suggest that the opposite of a previous statement is the case; on the contrary:
[sentence adverb]:
There is no shortage of basic skills in the workplace. Rather, the problem is poor management

[ODO]

Thus your sentence becomes

The casual encounters didn't work for me, though. Rather, each of them left me emptier than before, and made me feel guilty afterwards.

Solution 2:

The first suggestion in Dan Bron’s comment is very good: quite the opposite is a more or less fixed expression very common in colloquial speech. I would personally also be very likely to add in an in fact, just to enhance the juxtaposition:

The casual encounters didn’t work for me, though. Quite the opposite, in fact: each of them left me emptier than before, made me feel guiltier than before.

Another commonly used option would be to simply use instead:

The casual encounters didn’t work for me, though. Instead, each of them left me emptier than before, made me feel guiltier than before.

Yet another simple option is the all they did was construction (though that does make “each of them” very hard to work in):

The casual encounters didn’t work for me, though; all they did was leave me emptier than before, make me feel guiltier than before.

And probably the simplest of all would be just, though it does also downplay the opposition a bit and has slightly less ‘oomph’ to it:

The casual encounters didn’t work for me, though; each of them just left me emptier than before, made me feel guiltier than before.

As a side note, while I do get the rhetoric effect you’re going for with the parallel clauses, I don’t think it works particularly well here. If it were me, I’d just get rid of it and simplify to a single clause (using the last version as an example):

The casual encounters didn’t work for me, though; each of them just left me feeling emptier and guiltier than before.

Solution 3:

There are lots of formal ways of registering an alternative.

A simple informal method would be to, instead of replacing the term, rework it with 'but':

(blah blah casual encounters are great blah blah)... but they didn't work for me. Each of them left me emptier than before, made me feel guiltier than before.

'but' really means 'and here's an alternative in the other direction'