Honestly when I got a comment similar to this what I did was to search everywhere I could to find an editor, I personally don't take comments like that lightly. if it's in regards to art, screw them. every artist views themselves as developing ( at least I do) but when it comes to grammar, do the best you can to see if you can find someone who can do it for a fair price or you can set it up as a volunteer editing project. and when I did that, luckily I found a really good editor who was willing to do it for me free of charge and I compensated her with a drawn portrait of herself and acknowledgment on my main website and I also linked to her website. you can do something like that. that's if you want to. don't give up. if you can work on grammar do that. but as for art, you will naturally get better the more you draw so screw them. if they like your work they will stay. if they don't they can find something else to read. simple!
i remember when i use to get talked down about my art, i never let it get to me because I LOVE IT and ITS A PASSION. so nothing was going to change that. my hard core fans stayed with me and watched me grow. thats how its suppose to be. and its also ok if you leave because you don't like it. just keep doing what your doing