I began dating a veteran of Afghanistan about three weeks after his return. About two months into our relationship, my otherwise affectionate, attentive partner has begun to exhibit symptoms and believe that I am the cause of all our problems.
When I tell him I need reassurance about our relationship, he gets angry and avoids the topic entirely.
I am willing to stand by him through this, but I do not know how to communicate my own concerns.
It is not clear to me from your question exactly what the symptoms are that you are noticing in the behavior of your partner. Have other people noticed them, too? Does your partner see his behavior as changed since he has been in Afghanistan?
If you and he disagree on what is going on, it might be worth going to a couples therapist who can evaluate what is happening between you and can provide a neutral opinion. If your partner does have PTSD, you can reassure him (and yourself) that it is not his fault but a predictable risk of combat -- about 20% of returning veterans reportedly have PTSD.