I agree with the first part of this, though I have a different interpretation of the ending. I think that the relief Theo felt was more so to do with the fact that he could finally let go of the secret he held in for so long. Ultimately, although he did what he did, he is not a bad guy. His intention was to help Alicia heal, as well as himself. He never meant for the following events to happened in the direful way that they did.
By the truth coming to light, he could finally face the reality of the situation and own up to what he had done. He felt free from the burden of concealing the truth.
By the truth coming to light, he could finally face the reality of the situation and own up to what he had done. He felt free from the burden of concealing the truth.