The 30 year-old, who parted from actress Biel in March after nearly four years of dating, has insisted she is still the most 'significant person' in his life.
He said: 'She is the single-handedly most significant person in my life. In my 30 years, she is the most special person, OK? I just don't want to say much more, because I have to protect things that are dear to me - for instance, her.'
The Friends With Benefits star later hinted at possible reasons behind their break-up.
He added to Vanity Fair magazine: 'I think the mistake is that people commit to who that person is right then and not the person they are going to become.
'That's the art of staying together, is changing together. When you say it like that, it seems damn near impossible, right?'