As someone outside the situation, I can't say anything for certain and you have to be the judge in the end yourself. However, you need to be sure beforehand that you're willing and able to handle living with a significant other that has PTSD.
I would definitely suggest reading on the subject to get an idea of what you'll be expecting, while keeping in mind that different sufferers tend to have their own brand of suffering to endure. Try and recognize what reactions he has and let them know he's having them, sit down and have a talk once he's calmed down about possible solutions both temporary and permanent. I suggest you do everything in your power to get this talk out of the way before you move in together, so when things get complicated (and sometimes things WILL get complicated) you'll have an idea of what you can do to handle the issues that arise. Communication is the key to any healthy relationship with or without mental illness, but if he seems uncomfortable with the conversation let him go and try again later. However, don't let him go forever. At some point you do need to talk about this, and the sooner the better for your relationship and for everybody's happiness.
Also, as JustMeHere said, it is your significant other's responsibility to manage his symptoms to the best of his ability, and if you make this commitment it will be yours to help him recognize what he's doing and how to curb it. While you should not blame him for having the symptoms, you must not let that be a blank check to get away with whatever he wants. Let him know what your boundaries are, and what you can and can't deal with ahead of time so if something happens and he breaks those boundaries he'll know to expect you being upset as opposed to expecting you to be fine with it since he got a green light to continue with every other action he's made. It's important that you expect the same things you would in any other relationship for a sense of stability without making him feel attacked for being a sufferer. You need to be honest and assertive of your feelings without being aggressive or hurtful, just like in any other relationship.
What your friend said does concern me. "Why do you put up with that?" is not usually a question asked when everything is okay, and says to me that either something is unhealthy in this relationship that you do not realize OR she perceives it as unhealthy due to not realizing that your significant other is suffering from PTSD. Both are issues that need to be tackled, and you're the only one who can decide which is correct. If I were in your position I would definitely make sure me and my significant other sit my friend down and let her know what she's about to deal with. After all, if you're all going to be living in the same place she deserves to know what to expect when you two are living there.
And while I want to say you shouldn't move in together early in the relationship, I would be a hypocrite if I told you not to. My fiance and I have been together for four years, and we moved in together after only 2 1/2 months of dating. So hey, if you think it's right feel free, just remember that any relationship takes effort from both parties to improve themselves.
