Is she overthinking?

[Teachermammy]

I'm posting for a friend.

In her last relationship, her partner cheated physically, through messages and gave more interest to other women for the whole 7 years of their relationship.

Now she's in a relationship with someone new. He cheated on his ex once in the 8 years they were together.

While they were first seeing each other, but not officially together, he had slept with his ex multiple times and someone else. So that's not necessarily cheating but she feels unsettled by it knowing he had cheated on his ex previously.

But now all she thinks about is that he might cheat on her. They've been together a year now and she still thinks he might.

Any advice on what she should do would be great.

Depends on the rest of their relationship, how did this snippet come out?

No she's not over thinking, she keeps going with the same type of man. Huge red flags are flying in her face, if she ignores them then she's setting herself up for heart break again.

The new man slept around multiple times with other women when they were unofficial, well if a man really wants you, he'll make the best impression by only focusing on you and not sleeping around if he sees you as potential new partner.

No, she's right not to trust him, she's wrong not to have ended it already. The 'it's ok to sleep around with others at the start' is generally bunkum.
Sleeping with his ex - well this is a guy who thinks nothing of messing around with other people's feelings.