Bring it up as "can we set a date where we can talk about where we are with our relationship structure?" hopefully he'll get it without you having to spell it out to him. Your other option is to say "I know what I am about to say will violate our DADT agreement but I need to set a date with you when we can look at where you are at working through what's going on with you in respect to my having a girlfriend."
Everything will be ok in the end. If it's not ok it's not the end.