>When they both left for college, she broke up with him after 2 years to “focus on herself” and ended up dating another guy at her college after just 3 months.

"Focus on herself" aka the old "It's not you, it's me" routine.

>This is something my guy was hurt by because he said she thought she might’ve been talking/going out with the guy way before they broke up.

He's probably right.

>However sometimes if she comes up in conversation (another one of our friends went to high school with them) he will insult her or be like fuck her.

That's typical in the immediate aftermath, hopefully as time passes they'll stop bringing her up. And you can excuse yourself when they start talking about her.

>I’ve asked about her before and he had nothing but negative things to say, and told me about their intimate life (to be fair, I asked, so this was on me).

Correct. That's on you.

>The first time he brought her up, I defended her because it made me uncomfortable to trash talk another woman who I haven’t met and don’t know so aggressively, and I refused to agree with his negative comments.

Definitely not your place to defend her.

>Now I just let him rant or stay quiet if she is brought up. It’s gotten a lot less over the course of this relationship, but it still happens.

But you don't need to sit there and listen to him, either. Just be straightforward. "Dude, I don't want to hear about your ex." Point out how you two have limited time together anyway, so let's not waste it talking about her.

>He has however told me that the only way he can get over girls is cutting contact completely or hating them, which I feel was fair for this situation since he thinks she cheated on him.

Cutting contact is the right move, and he can hate her if he wants. But to keep talking about her he's only hurting himself. But that's his problem. Let him rant about her with his other friends, not you.

>Im not sure if this means he’s not over her or if he genuinely needs therapy/to talk this out with someone.

He's young and got dumped (from his first and only "adult" relationship), it's natural to be hurt and feel angry. I don't know if it's reached the level of needing therapy yet but, again, that's not your problem, since you're not looking for a serious relationship with him right now anyway. You should just enjoy the remaining time you have with him, for as long as it remains enjoyable. If he can't stop ranting about his ex around you, then you should cut your losses.

>And how do I hint to him that I’m not comfortable hearing about this anymore?

Again, don't hint. Say it.