Callum regretted his greediness.
He regretted choosing money over Clara, so he felt embarrassed and thought himself unworthy of her.
After the whole threat by Leo and how he actually thought of letting her go and asked his assistant to try purchasing some of the stock Leo put on the market, that was when his dignity to openly chase her was crushed.
He acted like the share mattered more, when his feelings should.
The guilt ate him whole, but he sealed it in.
But the more he kept seeing her the more his feelings for her got stronger, since Clara is now a shareholder and important figure in his corporation.
He would occasionally hold a shareholders meeting, just to make her look at him, but during the meeting, Clara will sit with her leg crossed and chatting with Leo on her phone, not interfering in their conversation.