Looking for some genuine responses, even tho this is PFA still value the opinion of several posters on here.

So I've been with a girl for a few months now, according to her we've been 'officially' going out for one month since I've been staying at hers.

Last night she mentioned how her ex, who she split with 2 years ago, called her out of the blue - but she told him to call back later, emphasising to me that it was because she has no feelings for him and loves me etc.

A couple weeks ago lay on bed, when she was in the toilet, her phone lit up with a WhatsApp text from some guy; it said "aww that's so cute", I thought nothing of it and that it may have been a family member or just some guy she knew.

So I asked her last night what her ex' name was, and it turns out it was the same guy. So I asked her are you still messaging him - she said no. I asked her why did I see his name on your phone a couple weeks back, she then back tracked and said she forgot that he had messaged her asking for a favour. At this point I obv became suspicious and pressed her on it. She showed me her messages from him, and funnily enough the text I had previously seen wasn't there, just a few texts asking her to sort out his car insurance along with a love heart kiss emoji from him.

English isn't his native language, and this is the reason she cited for helping him out with the insurance forms.

She kept saying that there's nothing there and that she would stop talking to him entirely if that's what I wanted.

Needless to say we had a big argument about it, because at that point I felt like she was twisting things and hiding something.

Am I overreacting here, or is this something that would be a dealbreaker for any of you guys who are in relationships?