I've already seen a post like this, but want to ask for my specific case.

My best friend and I love music since forever, and both wanted to be a DJ. Yesterday for the second time I had the chance to play in the biggest venue in my city, and it was fucking great, this time I had a lot of compliments from strange people and even more from my other friends.

So my best friend is an incel for about 5 years now, doesn't have a job and will to game. The sole purpose for him to go to this venue with me was to watch me play. After the set all I hear from him is that some random guys in the crowd were really hating my set, and that sometimes I looked like I was giving my life for the set, as I was doing a lot of work behind the deck (kind in a negative way too). Not a fucking word about music selection, technique or anything. Ok.

When we're with my girlfriend, I think that 90% of all the conversations he has is something negative about me, be my sneaker thst he doesn't like or if I say anything cocky he says something like "oh woooow ForeverInYou, what a stuuud" in a very ironic tone and with a lot of emphasis, like it's for everybody to hear it.

I think the worst thing is that my GF 3/4 times play along with him (even tho she tells me how he's not a good friend to me), which irritates me as I end being the subject of lot of conversations since he only talks shit.

I know is common for guy friends to roast each other, but to me appears he hates me a bit.

What I can do to my GF and him? How should I behave in this situations and how to avoid them?