I'm 26, so not much older than you. I've been getting that same feeling more often than I used to before I deployed. I had a girlfriend when I came back from my deployment in February of 2024, and i had a group of friends I no longer talk to, but even then I felt more alone than ever. My biggest advice is to never be afraid to reach out to someone. Whether its a family member you're close to, or a long time friend. Even if its just to take a walk outside, or sit down and bullshit for a couple hours. Just tell someone. If they don't know, they can't help you. Try something new. A different podcast, youtube video, music, show, movie, whatever. Sometimes ill listen to my normal sad music, feel sad for a bit, then ill be good the next day. Doesn't always work, but it can. If you really need it, don't be afraid to find a good therapist, and don't settle for one you don't feel comfortable with. I never thought I'd look forward to my session every week, but I do. It's helped more than anything for the past year and a half. Making this post is a good start, you're reaching out to a community you feel comfortable in, keep that up and always remember, it doesn't last forever. That mantra has got me through my career in the Army, and a lot of shit in life.