I'm not saying every single time they spent together Tom was the bad guy, just that I can name a few different instances of him not seeming to care much about Star's instances and so it wasn't a one-way street of Star being awful.
Ex. Star is having her monster integration party she's spent months on, Tom knows how important he is, and when guests are literally vanishing he's literally like "lol calm now bb, they're probably fucking, like we should do, now."
During Booth Buddies, which I'm not trying to argue was a cool thing on Star and Marco's parts (though both instantly regretted it), Tom is barely paying attention to Star before and after the kiss. Literally more focused on his pie. This was also something it seems Star invited Tom to since it's for her servants, so it just seems like he's not interested but is neither telling her that nor engaging with her much.
In Is Mystery when a bunch of monsters have, once again, vanished from Mewni after the clusterfuck of Mina's attack on the temple that Tom was actually present for, he once again doesn't give much of a shit about how worried Star is. He keeps asking her if he's better than Marco, and then tries to compare their relationship to the plight of the monsters just to get an easy kiss from Star in the end. There might be more examples than these three; these were just the first to come to my mind.
So I think they were both pretty bad for each other, and I can't say Star was "entirely at fault," let alone an emotional abuser. Star tried to talk to him about stuff she cared about a lot in S3 and he blew her off.
Did she avoid talking to him in S4? Yeah, but there was precedent on his part and Star was also in a really shitty situation. It's a good thing they broke up, then, but neither one was really a victim.
Tom also could've just manned up and ended it with Star as early as Lava Lake Beach. I think he could also be blamed for staying involved if he was unhappy with it for that long.