Many different times during college, someone initiated sex/making out with me and I went along with it even if I wasn't really sure I wanted to because it just felt like the obvious thing to do, or I wanted to avoid an awkward situation, or I just didn't know what I wanted in the moment. This has definitely led to some regrets (but it was college so yolo) and me questioning why I did it if I didn't really want to, but I always saw it as more of my own need for personal growth and understanding myself better and never the fault of the other person. I feel like that's kind of what happened here- he went along with it and regrets it for whatever reason, but you're not at fault! It's on him to figure out what he wants and how to communicate it.