I think it would depend on the relationship and your partner. If you are a boy as you say, I'd seek professional help, as it may well be too much for a child to understand or deal with; you shouldn't even have to deal with this yourself. :\ Hope you get some support.

If, however, you just meant "male" and are an adult, then ... I'd say that, once again, it depends on the relationship and your partner, but I'd also recommend telling her if you feel you two are very close and love each other, etc. If it's just a few days in, maybe leave it out. I guess it really just depends on what's going on over there - we don't have the big picture, unfortunately.

To be fair though, dude, if you're gonna be judged harshly by a woman, for you being human and being mis-treated by someone else, then really I would personally question the precious time you feel is worth spending with her. I talked to my ex about some messed up stuff, as she did with me, and you know what? The world didn't implode.

Best of luck.

PS
Sorry, just read your profile and it says you're "young", so I'm guessing you fall into the former category. I really think it's important you get some professional support, though, most especially because you're young and you are better to get help for this now, rather than wait years while it festers in your mind. I wish I had proper help when I was young; it would've solved a lot of problems, I reckon. >.<