That's the 'problem' so to speak: initiating may be the right or wrong thing to do, or be the right thing sometimes and the wrong thing sometimes as well. Besides PTSD, sometimes a person isn't up to sex for other reasons, too.
What I meant by initiating, I'd like to clarify, is this: pass by the other and, e.g. give a hug. Then continue to do something else. Ten minutes later pass by again and give a kiss. Do something else. Then come by, stand behind the person and stroke his hair, for example, for a while. That's about when the lights would go on in my little silly brain. ;) And I might turn around and 'chime in'. Or I might not, if I really weren't in the mood. Just words though, when I'm caught up in life, might not be enough. Also, words form a certain picture in my head and that picture of sex I might not want at all. But those little tender signs of appreciation, for me not too much and not too little, might give me another picture and may lead to sex more slowly, tenderly. A whole other thing for me.
With me, words always form a picture... 'Making love', for example, I can not even think. It's meaningless to me as an expression. Sex does form a picture, one that mostly makes me go 'ugh', although I actually like the real thing. Just saying.