"Romantic Suicide" has been categorized in old playwrights and literature. Particularly in Middle Eastern and East Asian cultures, as an act of rebellion against arranged marriages. In cases where the choice of marrying one's family pre-arranged partner was against the will of one and the other, couples in love would commit suicide mutually in an act of defiance. A romantic tragedy theme abound outside of Western culture.
As far as the legal mechanics, suicides are a matter of criminal procedure as far as investigations and processing of the scene of any non-natural deaths. I have no knowledge of suicides as an element which would frustrate any estate under civil procedure or probate court of jurisdiction. State laws vary widely on this. In some States it may be unlawful to assist or provide any means or inducement enabling another to commit suicide. However if both voluntarily and mutually commit suicide without undue influence, by their own accord then I cannot see any authority in the prevailing case law for any criminal or civil exposure. So as long as each individual acted independently, and took their lives by their own volition, on their own accord and by their own doing without undue influence and without any direct assistance by another, and both have died, there would be no ex parte liability on either's estates, trusts, or other probate matters to my knowledge.
In other words, if both acted jointly as they would have done independently, say by consuming a toxin or poison independently and without being influenced to do so by the other, the law would view both deaths as suicides by each owns volition. So as long as direct assistance in the commission of the act was not provided to the other, and each took their lives by their own volition and means, I find no authority in the case law that would make one legally or criminally culpable to the other, or frustrate any future potential estate or probate matters postmortem.
As far as the romantic element, everybody's feelings on this very widely. Some people want to die alone, others crave the company of another. Others would go as far as to have a last affair just for good measure. I can't provide legal advice however I would say conduct a background check on whoever you're going to meet, make sure they're not a serial killer or looney. If you like the person and are intent on dying together, make sure that you refrain from providing any direct assistance or lethal means (or leave no written or digital communication traces of the same). In case one party survives, the other may be culpable for providing direct assistance if such digital or written or other evidence is later discovered. That would be the only legal risk I foresee, they survival of one party potentially being culpable for the death of the other. So as long as both complete suicide jointly in the manner as they would have done independently, then there would not be any legal qualms in terms of family feuds which the law would provide for.
This should not be relied upon as legal advice, I'm not an attorney. This is only information, for advice you are very much encouraged to speak with an attorney and consult your local State laws.
Happy Fucking Valentine's Day LOL