I think Felix is a fascinating character in many ways. He's both repellent and transcendant, if that makes any sense, a braggart, a murderer, selfish and vain and also a person who was genuine in his charitable efforts. It would be interesting to know what Irina really thought of him. We know that Felix had to have bedded her at least once to produce the child. The daughter resembled her father. So maybe they had a more normal marriage than people think they did? The letter she wrote to him while he was planning the Rasputin murder kind of suggests to me that she knew him very well and could read between the lines and tell he was up to something.