Bad timing, have feelings for each other

My recent ex (mutual agreement) even though it was his decision to call us off, asked if we could remain friends afterwards, we were only together for 9 weeks. I couldn’t answer the question, because I know if I said yes I think it would be head games to me as I have feelings and he does too, but the timing I guess wasn’t right unfortunately because he is deploying for six months soon here in February as well as worries about opening up with his vulnerabilities, and he’s afraid like his past try the girl dumped him but I let him know I had weeks to think this through and decided to give it a go. However in the same breath, he told me weeks ago while in conversation that he doesn’t remain friends with former relationships, so I’m confused as to why he asked me? When I said idk if that’s wise, he got super sad, and his facial expression shut down too, I also didn’t get vibes he wanted to be FWB.