Ashlafriend.

As someone who used to have a BIIIIG problem with run-on sentences I can tell you what worked for me. I started simplifying my scenes/posts to ONE major scene per post. Not necessarily making SMALLER post per say, but smaller scenes. Think like a movie director or a video game director. Everything you place in a scene should have some sort of meaning to the story itself.

Run on sentences come with trying to fit too much in one paragraph.

A pro tip I learned from someone was ONE WORD can be a paragraph. Learn to keep your thoughts separate and you can work things from there. ALSO start working on constructing your scenes as if they were part of a Movie or a Video Game. As someone who is an artist, that helped me out IMMENSELY. Seeing the scene from the pov of a Movie Director/Producer/Writer/whatever you want to call it. The point is, simplify your approach to the actual posts themselves and you will be golden from there.

It will take a bit of effort on your part (I still do run-on sentences once in a while, but no where near as badly as before.) but I believe you have the potential to become a great writer. Just keep at it.

~Pav