Is one who lends money to his friend to open a women's accessories store sinful, knowing that the friend will sell to women?

You bear no sin for lending your friend money to purchase machinery that can be used for permissible or forbidden purposes. If you feel a lack of success, you should review yourself, renew your repentance, and seek forgiveness, for trials may be due to sins. As Allah Almighty said: "O My servants, these are but your deeds that I record for you, then I will pay you back for them. So, whoever finds good, let him praise Allah, and whoever finds otherwise, let him blame no one but himself." Sins remove blessings and bring misfortunes. You should also maintain the prescribed remembrances (adhkar) and legal ruqyah (definition).