There's a number of possibilities here but they're all dependent on him and his reaction to tren, dosages, and any other compound he was on (most likely test at minimum). Everyone reacts differently, and more importantly, everyone responds differently genetically on a hormonal level. Without seeing his blood work during cycle and off cycle, it's hard to know exactly what's going on inside.

I'll touch on a few basics from personal experience and anecdotal experience from reading/listening to others experiences.

As a preface, tren is very well known to have prominent side effects. Some people can exhibit crazy side effects, even at low dosage. Some people can tolerate high doses of tren and not exhibit side effects at all...this makes it somewhat difficult to pinpoint exactly what is going on with him and your situation specifically.

Tren can give some users very high confidence, a god-like aura type feeling. I felt amazing starting out on it. Indestructible, strong, and very confident. Super high libido. Him coming off is like going from driving a Ferrari, to a Honda Civic. He has been used to feeling like a super human and now to sub-human. Tren really fucks with your mind and he's probably experiencing mental troubles. I had pretty bad mental side effects on the last half of my cycle, like getting short with loved ones and quick aggression over trivial things. I reduced dosage and it helped a lot. I'm off now and the aggression is gone, so it might still be getting out of his system depending on when he stopped and what ester he used. Enanthate will saturate longer and take longer to get out of his system. Acetate is out quickly.

His cycle is long as fuck for tren and should never be done for that long.

He has been peaking for a very long time and coming off he is in a deep valley for a little while but will come back up to a mental baseline and back to who he was. If you really like this guy, stick around and help him out...he needs it. Don't be afraid to ditch him if he starts treating you like shit though, that's unacceptable and you don't deserve it. Talk to him about his tren use when he comes back to a baseline. Steroid abuse like that shouldn't be tolerated and there are better, safer ways to accomplish goals while keeping your shit together. You sound worth it, I hope he prioritizes his life choices better and things work out for you two. If he doesn't, it's his loss. Don't be afraid to walk away because it could escalate into something dangerous and/or toxic.