My best friend thinks her boyfriend is cheating, how can I help?

[seksek]

I really don't think he is, but she seems very worried about it. She's been cheated on in the past but has never been so obsessed with this thought before. They've known/liked each other for ~7 years but have both been in other relatinships. They have been official for about a month. He has cheated on every girlfriend he has had with her. I personally feel like that's only because in his mind it's always been about her, but then again I only know him through her.

This was our texting conversation today:

"jksdfhsjfhs hate everyone. I'm going to kill someone please love me"

"what happened?

"just angry today walked into (boyfriends) store and there's some pretty girl hanging out with him behind the counter and he saw me and told her to leave and come back later"

Personally I doubt this would really bother me, if they were openly flirting then yeah probably. But how do I console her? I know she really likes him but how is this healthy only a month into a relaionship? I don't know what to say to her

[BatDoc]

So let me get this straight. He has cheated on every other girlfriend he has had with this girl, and now this girl is worried about him cheating on her with other girls?

She should rightfully be concerned, however, she knows exactly how this guy is. And it didn't seem to bother her when she was the girl he was cheating with.

In the grand scheme, she's already decided he's cheating on her, so no matter what he says or does, she is still going to think that and find ways to justify her thoughts. So she needs to decide to trust him, although trust may be moot at this point considering the history between the two of them.