I have a problem with her past...

I have been dating someone I recently met online, and things are going great between us. We are taking things slow so we haven’t spoken about being in an exclusive relationship yet, but l am sure she will agree to it if I ask. What stops me is the information I now have about her past. She told me she once had an affair with a married man, after which I have begun to question her a lot. I don’t want her past to affect the present or a possible future, but I can’t help wondering if this means she has some questionable values. Is she dating material? How will I know if I am making a mistake by getting into a relationship with her?
You can either claim that her past doesn’t affect your present or choose to let it. Everyone has skeletons in their closet, along with questionable decisions. She could have chosen to keep that information from you but has presumably mentioned it because she is okay with her past. If you aren’t, there is always the option of talking about it, and letting it come between you and a possible relationship with this person. If you aren’t sure, take your time getting to know her a little better before proposing a committed relationship. If you decide to commit, do it with the spirit of openness she has shown, by acknowledging that her past is her business and shouldn’t impinge upon what happens between the two of you.

My boyfriend used to send me poems, and I thought he was the sweetest person, until I found out that he had sent the same poems to his ex. Should I dump him for lying?
Did he withhold that information or lie about it? The distinction is important. If you don’t like the fact that he has been sending the same poems, does it change how you feel about him? Do his acts or the way he behaves towards you give you any cause to question him?