Read other letters about this article
After a death--and a breakup--things are likely to be a bit chaotic. There's nothing that says the LW can't put the money away where neither s/he nor the partner would access it until a set time (like a CD, for example). The passage of time would allow the LW to make a decision s/he could live with.
The ex's behavior-cheating etc. and probably spending their joint money on flings makes one have no pity for the ex, to be honest. in addition, there are other ways to 'return' the money to the family.
For example, the LW could start a 529 (I can't remember if that's the correct #) account for the Ex, and put the money there, so that he can only use it for school expenses. Or, the LW could start a similar college fund for nieces/nephews. i.e.--The money could go back to the family, but in a way that the LW could control, so that the Ex couldn't harass the LW or other family members for the money.