Is it bad to think negatively about your friends first and new relationship?

Hello! I have a friend who I grew up with and I see her at her worse and now she is finally happy. I saw her went through everything, she have a shitty life, she always feel forgotten, she's a middle child and the only daughter. But now she is in a relationship with a guy we met on the internet and she's happy. They met last year and they met up this January and I went with her, the thing that bothers me is how the guy reacted when they first met. I saw how excited and happy she was while the dude is just standing there awkwardly. It planted something in me that I need to be on guard about the guy. I'm happy for her but I'm afraid that my negative thoughts are true. Especially now that she gave her first everything to him. I'm happy to see her happy but I'm scared for her. I told her that I don't fully trust him but she knows him best so I'll trust her decision.

How should I handle this? Is it bad that I am feeling like this?