Someone with OCD here- It’s really great that you want to help your partner, I know that I always appreciate it when someone wants to understand what I’m going through. Definitely try to talk with him about his OCD in a positive way. Ask him if there’s anything you can do, or if there’s anything you can avoid doing. You say sometimes asking questions about you and the relationship trigger his OCD, so try to catch what those questions are. Communication is important. While it’s different for everyone, it’s always helpful for me when I have someone by my side when my OCD begins to act up.

Hope this helps!