Since some think bajaj might be turned into a villian I decided to leave this here.....
 Bajaj to his family is a protector, shield and provider. With taanvi he is taking care of her studies it seems, with kuki he is the best father in the world, for the aunt he is the best son who solves all problems and now with prerna becoming a part of his short family he is the best husband. The writers were very careful to show this. This is not an act this is him being very genuine. As he cares fiercely for those part of his family. 
Anyone who threatens his family or crosses their limits he teaches them a lesson without crossing his limits. He will not let his family break up no matter what. And anyone who threatens that he takes care of them. For example with taanvi he told her if she can't stand prerna he will send her overseas hence eliminating the threat to his family. For A he withhold himself greatly. He gave him chances and A took advantage of that. A planned the accident and bajaj took advantage of it and did what A wanted. However he stayed within his boundaries as he told A. 
On one side you have bajaj being a perfect husband, father, family member and the other he is a cold ruthless person to his enemies. 
Komolika will definitely try something to harm prerna and again bajaj will be seen as the hero in prerna eyes because his feelings for her is genuine. As well as when they introduce menaka she will also be a villlian who will cause trouble for bajaj and prerna but again he will be seen as a hero. Not to mention his father being abusive and beating him when he was a child. Which is why he does everything to make kuki happy and not feel pain.