I agree with hotgirl here...there is alot more to this than she is telling you...
have you ever tried to have sex with no lube? that is like someone trying to pull your insides out thru your vagina!!
even if you do try and work things out...this has been going on too long for you to stay and subject yourself to this happening again.
once a cheater....shall I go on?

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Don't know.....do ya??