1. Thor and Jane Foster broke up
The relationship was confirmed to be over in Ragnarok, and it's unclear on what sort of terms the two were on as Thor explained to Loki it was a mutual break up. Endgame also brought to light the fact that Jane had been blipped by Thanos, and so there's another five years at least that the pair were estranged. Given the title of the upcoming release and Jane's prominent role in the film, it wouldn't be too presumptive to say their relationship might not be dead in the water just yet.
2. Korg
The two first met in Ragnarok in the gladiator's quarters. Since then, the pair have had a close friendship, with Korg often helping out Thor in times of need. Korg, a Kronan, was seen in Endgame playing video games with Thor in New Asgard, so they clearly stayed close during the "blip." The last we saw of him was back in New Asgard, but recent trailers have featured him, and so we can definitely look forward to some more comical scenes between the mismatched pair.
3. Thor's Dad Bod
The God of Thunder was renowned for his impeccable physique prior to this. When Endgame finished, Thor was still in this dad bod phase, but the trailer for Love and Thunder has shown us how he has transformed back into a more recognizable version of himself. This will allow him to be taken more seriously, although his humorous quips don't seem to have gone anywhere!
4. Thor is currently with the Guardians of the Galaxy
We last saw Thor at the conclusion of Endgame. After passing over the title of King of Asgard to Valkyrie, Thor boarded the Guardians' ship and set off into space with the crew. It's unknown at this point what they have been doing in the time between Endgame and Love and Thunder, but the presence of the Guardians in the upcoming release should enable us to get some answers. One thing we know the Guardians, or more specifically Starlord, wanted to do is find Gamora. It'll be interesting to discover whether this has any bearing to the story in the fourth Thor film, but we should be guaranteed some entertaining exchanges regardless.
5. Loki is Dead
Loki was killed by Thanos in a heroic final stand. After trying to convince Thanos that he would help him, Loki tried to stab him in the throat. Unfortunately for the demigod, Thanos saw this coming and prevented it before grabbing Loki by the throat.
6. Thor now wields Stormbreaker
After losing his signature weapon, Thor needed something new. Enter Stormbreaker. The mythical ax was designed by the dwarves of Nidavellir to be the greatest weapon ever created, but was only finally made when Thor came looking. With the help of the Guardians in Avengers: Infinity War, Thor and Eitri were able to create the mythical ax.
As well as being able to channel all of Thor's powers and exert monstrous blasts of energy, Stormbreaker can be used to access the Bifrost, which allows Thor to teleport across the Nine Realms.
7. Mjolnir was destroyed
Mjolnir, his infamous hammer, was shattered by Hela. This showed off her true strength as she was able to smash the "hammer like a piece of glass," as Loki so sympathetically put it.
8. Valkyrie is the ruler of the new Asgard
In the conclusion of Avengers: Endgame, Thor told Valkyrie (Tessa Thompson) that she was now the ruler of Asgard. After firstly mistakenly taking the comment as a joke, Valkyrie realized that Thor meant every word. Thor didn't want to live the life he was expected to live, he wanted to forge his own way through life, and so the mantle of King of Asgard was not one he was willing to hold. Before Thor left, Valkyrie explained to him that she would be making many changes to New Asgard, something that will be interesting to see in Love and Thunder.
9. Asgard was destroyed
After an uphill battle against Thor's mightily powerful sister, Hela, Thor and Loki had no choice but to release the fire demon Surtur. In an epic final stand, Asgard was completely destroyed and Thor could only look on and watch as the place he and so many called home burn down.
Now, that you've brushed up all the facts from previous movies, you can rush to the theatres. If you're looking for Thor T-shirt , here's one you would love.