That seems a bit petty of them to me.

Who knew! Hard work and practice and all your time and effort put into art can actually pay off! WHAT A HORRIBLE THING!
I really don't know what to do about it... bad with that advice. But hopefully it's not getting to you! Anyone that wants someone to feel guilty or wrong for making something of a developed talent or skill is wrong. : /

It's starting to make me uncomfortable, mostly because my friend gets to hear all the shit :0 and i really don't know how to react

I feel like it's mostly your friend's place to tell them that they don't want to constantly hear their friend slandered, then.
Life's got too much negativity already! Spending so much time and energy on tearing someone down for literally no good reason isn't high on anyone's list of things-to-enjoy-today.

I would honestly say confront them. Ask them why they seem to dislike you and point out that you have been kind and civil to them for the most part. Then Just express that it unsettles you that they would seem to dislike you so much when you don't know the reason. I'd also probably mention that you don't like being shit talked about and that it's okay if they just dislike you but talking shit about you is inappropriate and immature.

Not worth your time leave the person alone let them feel jelly that your better than them.
If it gets even worse bring out the british insult card hah jk dont do that

Just ignore the jellyness and i agree with jester here its should be up to your friend really

This definitely is a complicated situation. I am really sorry you have to be dealing with this, and that your best friend is tied in to the problem.

The person couldn't avoid exposure for long. Something I would only hope to try and see is, they may be very troubled. They may struggle with that vice which is likely envy, towards you, and anyone else that arrives to their awareness about what they do, to in concept render them in a complicated evaluative state about their own doing. There may be a lot of subject to comparison, but a lot of it is negative no matter what. It's not good that this is happening, the person is not in the right to be treating you like this, and this likely needs to be confronted right away.

Personally, I would leave a note for them either by direct message in saying hello to them again or in meantime in offering kindness and your valuable person of expression. Let them know finally about your knowledge of things as your friend does and try your best to be understanding. You can let them know about the power of acceptance and possibly be a reminder that what they do is as appreciated as all the other wonderful work that is illustrated and shared among one another. If there are issues that continue on from an eventual confrontation of the matter, let them alone and move on. Your friend will be there to follow I'm sure. It already seems that things have heightened from complimenting. Only so much can be done sometimes, and it's not welcome for negative, demotivational people to be involved with your life.

You are an amazing artist. You are loved, other people out there definitely need to know that. I am hoping the best for you on this, I believe that you can do it and it will be okay.

It can be a really rough situation, because I think its just in our natures that a lot of times we want to just step up and nip things in the bud and just confront and fix things. Truth be it does sound like its something your friend should probably be the one to tell the person they don't feel comfortable being a a vent box on that subject. I have found that usually the more folks one gets into a situation (as each person is going to have their own perspective and insights to a situation), the more complicated its likely to get. So it may be a case that your friend if they feel uncomfortable by the person talking trash...they are going to have to tell said person they feel uncomfortable by it. And if you do feel uncomfortable about them talking trash behind your back, perhaps being direct is the way to go as it may also just stem from their own insecurities and feeling the proverbial grass is greener and if they realize you are not an anonymous art-force but a person who has insecurities of your own it may help bring some closure.

(Sorry for all the typos and prolly so-so wording, just woke up so brain is like sloooowly reboooting XD)