How should a young man act who secretly married an older European woman who converted to Islam, and they had a child, while his family is completely unaware of this matter, and he feels lost, wishing to please his parents yet not wanting to devastate his wife?

You must offer sincere repentance and separate from that woman, as the marriage contract is invalid because she was still married to her first husband and because of the absence of a guardian (wali). It is not permissible to abort the pregnancy, if one exists, and the child will not be attributed to you if you were aware of the unlawfulness and invalidity of what you did. However, if you believed the marriage to be valid for an acceptable reason (such as being a recent convert to Islam or being far from scholars), this might constitute a doubt (shubha). You must explain to her, through your female maharim, the invalidity of the contract and the impermissibility of you both staying together. You should also guide her, through women, to righteous company and someone who can teach her the rulings of her religion. Furthermore, you must renew your connection with your parents and turn towards acts of obedience.