It's not really surprising. Yeah he needed help to get out, so did she. They helped each other to try to get out, yea he did have some bad ideas but he was built to make bad choices.. doesn't mean he was manipulating her (manipulation would normally takes more smarts than he had). A lot of people agree getting attached to glados's body changed him for the worse. His AI just like a person, has its good side and bad side. The power fed on his bad side and corrupted him. Outside of that I think him and Chell were becoming friends, as people tend to latch on to each other in dire situations.