My partner (22F) seems to trigger my nervous system every time she does something. Do you have any advice?

Hey, I’m a 23-year-old guy, and I've been in a relationship with my girlfriend, who’s 22, for about eight months. We've experienced some significant highs and lows, primarily due to our differing attachment styles—I'm anxious, while she tends to be more avoidant. No matter what I do, I struggle to trust her and feel secure in our relationship. I think this stems from her fluctuating behavior; she can be incredibly warm one moment and then distant the next. Our busy schedules mean I can only see her once a week, which adds to my worries. Today, something happened that really triggered my anxiety. I was on VSCO and noticed she had reposted a picture of another guy's dog running on the beach. She's never mentioned knowing this guy, and it freaked me out, especially since she’s never shared any photos of me or reposted anything I've posted. I can’t help but wonder if it’s worth being constantly stressed over someone I care about. Another issue is that whenever I bring up something that bothers me through text, she tends to shut down and ignores me for days. This means I have to bottle up my feelings until I see her, which leaves me anxious throughout the week. I’d really appreciate any advice on how to work through this. Edit: I’m also concerned about looking foolish since I’ve invested so much time and let things slide that I shouldn't have. I want to stop feeling like I'm being walked all over, but I’m uncertain about how to change that.