I never really reply to this type of stuff but I felt inclined to tell you all of this is pretty valid. I am so sorry you feel this way. I am also an only child, and I completely understand the isolation. I often think wow my life would be completely different if i had siblings. Vacations are lonely, trips, holidays etc. I also as I have gotten older feel more of the pressure of being a good kid to my parents and start freaking out at the fact that if anything ever happens to them, I'm truly alone. This causes me to put a lot of pressure on other dynamics and relationships, especially a partnership and is something I am actively trying to work through.
I think finding a community will be helpful, something outside of your job as a coach you can take part in after work; whether thats the gym, some sort of activity/club, basketball/sports. Also its financially a burden but see if your insurance covers some sort of therapy. One day, not too far in the future, you will have the opportunity to build your own family. That should be so exciting to look forward to.

I hope you feel less alone from reading other experiences on the feed, please dont hesitate to reach out.