My gf lied to me in the past, married people pls help

My gf 25yo lied to me when I confronted her about talking to her ex and a guy she once had a fling with. I confronted her when I saw text messages between her and her ex because she called her a pet name according to her everybody in her friends group called him. He texted her wishing her a happy birthday with. A lot of smiley faces and a big text and she kind of responded the same way. Then she wished him a happy birthday and a few smiley faces and when I saw that it got me pissed but she said she didn’t find anything wrong with it because they were just birthday messages. The other guy she first deleted the text messages between them (it was all confronted at the same time) where he called her a pet name and she answered with “hello my honey😻 etc… keep giving news” (in Portuguese) (but by the looks of the conversation he would text her on ig but she wouldn’t reply.) So I asked about it and she said she didn’t have any messages from another person. I insisted that she told me the truth and she kept denying it until I showed her the screenshots. She started crying and said she knew it would mess up the relationship because we were already fighting about her ex and I actually had broken up with her but after a few days I ended up forgiving her about it and we had a relationship again. I was talking to my best friend and few hours ago because this whole thing popped into my head again and he told me that he didn’t like at all what my gf had done and that he only even says hello to her because we are together if it was just a friend he wounds even talk to her at all. That was something very bad what she had done.
I’m kind of having second thoughts about this relationship and I really need some advice because I truly had intentions of marrying her from the beginning of this relationship.