Military relationship

To give you a little background. My boyfriend is currently stationed in San Diego and I’m in Miami Florida. So we’re currently doing a long distance. We’ve been having troubles lately specifically with a girl he hangs out with. I don’t know if it’s me overreacting or something I should be concerned about. I’ve been dating him for 4 years. I’ve never been the type to stop him from talking to anyone or anything in that nature. I know he has female friends but this one just rubs me the wrong way. Lately he’s been spending a lot of time at this one girls house. About a month ago he sent me a snap of some of his stuff that he said was a coworkers house in her house. We talked about it he said she’s a close friend and that’s why he has his stuff at her house. So I’m like why lie about it to begin with? He claims because he didn’t want to upset me. Then last week he sends me a snap of him in a bed, that’s clearly not his bed. So I confronted him about it and he said yes he was hanging out in her room. But I told him how I felt about that, that just didn’t sit okay with me. I told him I didn’t feel comfortable with him laying in her bed watching tv is what he said. Today he sends me a snap in her bed again after not replying for an hour. He said he took a nap in her place because he’s tired and he took a nap with his dog ( that she’s taking care of for him because they’re not allowed dogs in the barracks) now he’s currently still at her house while he does homework. We had a huge fight about it and he basically said that I shouldn’t overreact.

Update 10/29:

I wanted to get on here to update my current situation. Thank you to all the ladies who commented on my post and gave me advice! We were having issues and I put my foot down I told him it’s either you stop disrespecting me or I’m going to walk away from this relationship. Because I will not stand for him not respecting the boundaries or any possible cheating. That conversation ended with him being upset because I’m “thinking bad about him”. Then a few hours later he tells me he’s sorry, that he doesn’t want to ever disrespect me and that he feels selfish for not listening to me. He also apologized to me and asked I have every right to think poorly of him for lying to begin with. So he suggested that I go visit him in San Diego with a week or two to meet this girl. He said I could be upfront with her, ask her anything, etc. He said if I don’t like the girls vibe then he’ll no longer talk to her and that I can take the dog with me. He swears nothing happened between them and that’s why he wants me to go, to have clarity and to spend time with him. Thoughts?