Is a boyfriend is suddenly ok with an open relationship, is this a bad sign?

Anonymous

We've been dating for 3 years now (I'm 25 and he's 29). Last month was the first time he suddenly suggested that if I wanted to add a 3rd party I could and it wouldn't be cheating. He's said he would be ok as long as I follow 3 conditions: My boyfriend is my only real partner, I never develop feelings for the 3rd party and it's not with one particular guy he hates. I'm his 3rd girlfriend and he's never been like that with anyone. He admitted I'm the only woman he is telling me this.

Needlessly to say this quite took me my surprise. Is this a bad sign?

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This doesn't seem like the common, normal reaction a loving and protective boyfriend would feel towards the woman he loves. Typically guys are territorial and jealous in that aspect. They usually don't like sharing their women, just as they don't like sharing their cars.

If a boyfriend is ok with it and doesn't seem to care this is a bad sign right?
Is a boyfriend is suddenly ok with an open relationship, is this a bad sign?
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