From my limited understanding, I think you cannot sue him. Here are my reasons:
1. You are 28 years old now. About 10 years back you were 18 years old - a Major, having a capacity to earn. So ideally you could have earned your living without being dependent on your father.
2. Even if it is argued or considered that it is parents responsibiliiy to look after the kids till they attain majority, your mother was there taking care of you. So nowhere in law it is told that "both" parents should take care of their wards.
3. Now thinking about the argument from your father's point of view, he will clearly question your locus standi. He will say legally speaking you have no right to question him. He will say your mother has all the right but you on the other hand have no right.
So from my understanding, you cannot sue him directly. If at all you want to sue him, you have to go via your mother.
Having said that, suppose if you have inherited any property, which your father sold without your permission, then you can sue him as he has not spent it the amount on you for your welfare. So think if you can make use of this.
Now playing the Devil's Advocate:
In your question you say "For the past one year I've been accompanying and assisting my mother in filing lawsuits against him for maintenance, bigamy etc., and I've had to forego two years of post-graduation owing to these pressures, psychological and financial.".
You say that you had to forgo 2 years of PG as you had to run around with your mother filing law suits. So it can be that one fine day you decide to sue your mother also, saying because of the pressure you could not pursue your PG.
Don't take me wrong here, it's just that I am saying that you don't have a proper ground to sue your father.
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