hereorthere: Listen to oomis.
There is indeed a shailoh whether or not one may marry a ba’al tshuva, because of the ‘ben nidda’ suspicion. However – Rav Moshe Feinstein wrote in a Tshuva (responsa) to this question that the shortcoming of a ‘ben nidda’ would be apparent in the person’s middos. Hence, a ba’al tshuva who has fine middos is clearly not a ‘ben nidda’ and his middos prove that through some means his mother must have done t’vilah, albeit unknowingly (e.g. a swimming pool).
Is the inverse also true, i.e. does an FFB with bad middos prove that his lineage is flawed? Rav Moshe does not say so, but as we know from Pirkei Avos/Mussar sefarim – a person with Torah learning/fine middos is a better person in the eyes of G-d and His people than a person without Torah learning/fine middos, regardless of his lineage.
Go find people with good middos and live among them instead.