Asking in the wrong place. Anyway, I might be able to help.
The main thing you have to realize is that any relationship will have turbulence but it's how you handle the turbulence that matters. Service comes before you. It sounds really shitty but it's the reality. You signed up to be with this person and like anyone else, they will have their good and bad. You have to accept the circumstances for what they are and work within the frame if you want things to succeed. The relationship is not about you, or him, it's about what you created together.
He says that my constant need for reassurance from when he first got there/before he left has made him feel hurt. I've apologized for the negative effects of my insecurities and am actively working on self improvement things. I asked what I can do to lessen his hurt and he said "I honestly don't know".
He's saying he honestly does not know how to communicate with you further that you asking for reassurance, is tiring. He's asking you to stop. He is telling you he is not someone who can handle heavy emotional things- and that is completely alright. Now you have this information, you need to work with it. Stop using him as a means for self validation. You and only you, can make yourself happy. You are the only person who can actually validate yourself. You own your own feelings- not him, not your friends, you.
When you have this break, you should sit down and take a look at your insecruities. What are they and why are they there?. What can you do to improve them? They are clearly destroying your quality of life. He is not the answer. A relationship is not the cake, it's the icing. Sometimes maturity helps get through these things- other times, experiences. Consider counselling if it is actually severe. They will teach you useful techniques in dealing with stress, wellness, and managing your insecurities (mindfulness for one). I see you're already on your way there apparently, so take that weight off of him. He is not your crutch, he is your partner.
he texted me freaking out saying our recent relationship issues have caused him to lose trust for me.
Don't communicate anything important over text. Just don't. Fighting while he's deployed? Postpone it or just agree to disagree. If it's short time, just don't talk. If you can't handle not communicating for long periods of time, you might be in a relationship that is simply incompatible with your needs.
Sit down and make up some guidelines between you two. What is and what isn't okay. If you can't have this conversation or think you both just 'know'- you should reconsider. This is my opinion but a relationship is like a contract. Make up the guidelines, agree to them, honor your agreement and if someone fucks something up- reevaluate the basis of the contract, forgive, or walkaway. Clearly, those pictures bothered him and you did not know they would.
In your defense, if you didn't have this conversation about what is okay and what is, the claim of losing trust might be out there. Miscommunication.
he texted me freaking out
I'm going to guess you're pretty young. Don't want to sound condescending but I'm going to give you a piece of advice that will probably serve you. Under no circumstances tell others your partner is "freaking out". Don't use terms that imply other meanings. Your wording matters. It's like when a guy tells a girl she's being 'crazy'. It belittles their emotions, beliefs, and thoughts. It's disrespectful.
It's just that my insecurities and distance period and petty arguments have eroded a great relationship to constant arguments.
You can fix your insecruities, you can stop the petty fights but you can't change the direction or nature of this occupation.
No, this isn't the end. If it is the end, then you obviously avoided a bullet being with someone who doesn't have a stern enough spine to break up with you. Honor what you agreed on, start your reflective process, reconsider your actions from his perspective, and how you can alter your behaviour to help him cope. In addition, if he is doing something wrong, now is the time to speak up. Pick and choose your battles wisely.
basic, AIT, general distance and now deployment
This is the tip of the iceberg and just the beginning.
You can't ever fully understand another person but you can craft together their personna in order to blend your personalities for a successful relationship. Using empathy in order to 'win him back' is manipulative. Using empathy to restore harmony, is productive.
Finally, when you love someone- it is not you love them. It's that, they are loved.