Bottoming Problem

My boyfriend and I have been going out for about 7 months now and we like to explore different things sexually. One of the biggest issues that we have been having is him trying to bottom after being a complete top his whole life. He finds it extremely painful and despite trying things like AnalEze, rimming and massaging down there, it still seems like too much for him to bear. His painful facial expressions also make me limp, which only further adds on to the issue. Do you guys have any recommendations for us? Any advice is greatly appreciated!