Really fed up with my colleague and possibly my job. Am starting to doubt am cut out to be a developer

Am a junior java dev , been working working for this company for about 2 years now. Although they hired me to be a java dev, they pretty much exclusively had me working on JavaScript crap because none of the other more senior devs wanted to do even so much as poke JS with a long stick....

Oh and the salary was crap but i figured since i had barely 3 years of exp i thought i would stick with it for a while

But a few months ago after seeing other opportunities I got fed up and threatened to quit , already started interviewing etc
Got an offer, not exactly what i wanted but better than where i was. Went to quit but they freaked out and started throwing money at me. They matched and exceed the other salary and promised to addressed the issues that made me want to leave. Ie get me to work more on the java side of the project and have me work with someone more senior who could sort of mentor me, i had been working semi solo on the js shit till then...

The problem is that my supposed mentor is selfish prick... he is the sort of guy who comes in real early, basically he goes to early morning prayer then come in at some ungodly hour and fuckoff home around 3pm

He does all his work early morning then spends the rest of the day with his headphones on stealthily watching youtube, amazon, watching cricket, reading about Palestine , how oppressed muslims are or building a website for some mosque.

I asked him to let me sit with him so that I could just learn how this or that part of the sys worked , he agreed then the very next day comes in and does all the work before i get in at 9 , i asked him how he did it and he tells me oh just read the code.

Its not as simple as that, out codebase is an old pile of non standard legacy dog shit. Nothing works as it should, i tried to go through documentation online for the various stuff we use , but invariably get stuck when i try the usual approach because it turns out the original devs had essentially done a lot of custom hacks and cowboy coding to get stuff working, they screwed around with some of the framework jars & edited libraries to get stuff to work, resulting in some really weird OSGI errors.

My point is that i cant really just "read the code" or google ...
I gotta know a bit more what was actually modified and a lot of this knowledge isn't fucking documented, theres a lot of " ohhh that weird bug yeah yeah that happens cuz x did this hack some years ago to fix this issue and we kinda built on it, yeah we weren't supposed to do that but heyyy what u gonna do, just do this or that instead"

I was asked to set up a web service to export something, since thats his area of expertise and he is suppose to be teaching me the ropes, i asked him to explain where i should start and what would the general workflow be, his response is to tell me to just copy the IMPORT service and rename it to export then "just do it um change it or something" very helpful indeed (building enterprise application here nothing complex at all!!)

He sits right next to me so i can see how much works he actually does, i know when he just idly sitting there so thats when i ask him questions, he always has his earphones on so each time i gotta find a way to get his attention with a poke or a wave, he will give a heavy sigh and a weary look as he removes his headphones, listen to my question then give me the shortest answer possible before IMMEDIATELY turning away and putting his headphones on as fast as possible regardless of whether I actually understood or even heard what he said. If i ask another question ( am talking like an immediate follow up question for a clarification or something) he will
Do the whole sigh + tired look routing to make me know yeah you are disturbing me. ( god was so happy the day he accidentally sat on and broke them)

Yesterday i caught a glance at his screen as i was sitting down and i think he and another dev were talking about me
That am slow with my work and take forever to get into gear.

Starting to have doubts about my own ability n wether am really cut out to be a developer. I know i can work hard but its impossible to do so when you have no clue where to start and unable to look it up since all the custom hacks doesn't really allow any frame of reference.
Feels like am being handicapped and mocked, yesterday i just picked up my gear n left the office.

I never talk ill about my colleagues, whenever i have a 121 with my mgr i always all is fine, x n y are really helpful etc
I tried to indirectly tell my other colleague about this guy, he told me that guy had kinda mentally checked out of this job and was just going through on auto pilot and just laughed it off (they have been working together for almost a decade and a buddies) my other colleague is pretty nice but he usually swamped with work so i feel bad to trouble him.

Am really Fed up with it all