It's a fact that Shinji had feelings for Kaworu and Kaworu had feelings for Shinji. They straight up say that they love each other in episode 24. It's specifically romantic.

The definition of the word 好き, which is the word Kaworu used in the baths and later Shinji reciprocated, is:

&gt; 1. liked; well-liked; favourite; favorite

&gt;  「ケーキはお好きですか」「はい、好きです」

&gt;  "Do you like cake?" "Yes, I do."

&gt; 2. in love (with); loved; romantically interested (in)

&gt;  実を言うと、私は彼が好きでないのです。

&gt;  To tell you the truth, I don't love him.

The second definition is what is meant when you say it directly to someone. So, yes, Shinji does directly reciprocate Kaworu's romantic attraction. It can't get much more straightforward than that.