I [21/M] am a jealous boyfriend and I can't figure out why.

Hey everyone. Long time reader first time posting so please forgive any noob reddit mistakes.

The situation is this. This is my second relationship (with 21F) and we have been together for 12 months. First relationship was 4.5 years when my girlfriend decided she no longer liked me. Six months of struggling to hold everything together by myself until we broke it off. 6months break before me and my current partner start dating. She's an amazing woman, currently overseas for a few months studying.

My life quality is great. I enjoy my work, I have a wide friend network (albeit not many friends I would casually visit), but I moved out of home and don't really have family.

Point is, she will tell me things like she is about to go out with friends and hit the town, or she has guy friends come over and iron with her, or she will have 'seen' my message on facebook but take a few hours to reply. Each of these things eat me up, and make me feel like shit. All I do is send short passive aggressive messages back and I hate it.

I've recently started getting concerned that I have depression (mother has had it) but all aspects of my life seem pretty dandy, except maybe my relationship. Everything's good on paper, but I find myself feeling poor even in good situations. Similar things has started happening with friendships too (be hanging out with a group of friends when suddenly brain decides to let me know that they don't like me and all like each other more etc and so I leave).

I'm not sure if this is really the correct subreddit to post this in, but I'm just looking for some advice. Any advice will do, and I thank anyone who takes the time to read this.

tl;dr have a good life, dating a good girl, but feel shit. I get jealous or worried about little things and just want to discover what's causing the issue, or at the very least try and improve myself and be a better partner.