It really depends on the individual states, but I think that in this situation, if there's been no case or support order so far, it would be BM's decision to file a case if Dad wishes to get involved again. So if your fiance takes the chance of getting involved again, BM could file if she wanted to, then he would be required to pay, at least to the date she files the petition. I know this sounds sh**ty but if you two are in a tough spot financially, then Dad may want to think hard about if he really wants to "open that can of worms" so to speak. It's hard to say what BM would do without knowing her personality, maybe she would be willing to be civil, but never bank on that......good luck!

And of course this is just my opinion. From my experiences, common sense, and from the MANY boards of this nature that I have read, the worst thing that parents can do regarding their child is to take actions which benefit the PARENT rather than the child.
It seems there is something wrong with the notion that your BF would base his decision to get back into his son's life on the question of support. Alternately, if he has not been involved in his son's life for two years, his son is likely to have gained some measure of adjustment to his fathers absence. I think your BF needs to seriously consider the effect that re-entry to his son's life will have on the son (indeed its effects on the BM, as the son will be witness to that). If he is thinking of seeing his son again because he misses him now, that hardly seems a fair reason. If he is thinking of not seeing his son because he will owe past support, that should serve as a warning to you!
My BF has seen his daughter religiously according to his visitation schedule since he and BM were separated. His daughter has never known life without daddy being there at least IN PART. And it is STILL extremely difficult for her to deal with. The problems she encounters with having to move between houses, and deal with BM's anger toward her father are causing very real problems for this four year old girl. I don't know how old your BF's son is but my thought is that the older the child the more complex its thought process and consequently the more emotional turmoil will ensue.
Think of this child first. Frankly, BF should do everything in his capacity to pay child support before making any attempt to re-enter his son's life. Anything else would be selfish. My BF, sitting next to me as i write this wishes for me to add:
Both entering and exiting a child's life is an extremely emotional event for that child. If one is not prepared to make the commitment to do it FOREVER (either leave or re-enter) then they should not do it AT ALL. And if BF choses to do it, he should be prepared to "put his money where his mouth" is because being a parent is a financial responsibility as much as any other. Just my 2cents.

Yes she can get the child support for the past two years and currently. read my other post to your first!
And I agree, with someones post up there, if your BF is wanting to get involved ONLY if he does not have to pay support that does not say a lot for his character, and you may want to think about having a child with him yourself? What if he left you? With a child? You would want support for your child, right? This woman deserves his help in raising there child that he helped bring into this world.

Happy

" make sure you tell the people you love most EVERYDAY.. Its important not only for them to know but for you to tell.. Life is to short to be miserable..

What does it say about him if he hasn't seen his son in 2 years? Financial support is a way of supporting a child that he help to make. Is it fair to the BM to have to raise her son alone physically, emotionally, and financially? If he can go years without seeing his son do you really want to have a child with this man? In some states the custodial parent can waive the back support. I know in Arkansas they can. What is really hurting his case is that he hasn't supported the son for two or more years. If could show some receipts for items purchased for the son then the judge would consider that a means of support. I just want to tell you this think long and hard before you have a child with this man because it is not hard for the shoe to be on the other foot.