Hi,
There is nothing really remarkable about the synastry or composite, except the huge stellium in 12th. The explanation is karma. A stellium in 12th house means in their most previous past life, they were partners of some kind. And the saturn opposite means that they had lessons that they had to be educated upon, that they did not fulfill.
Danger wise, I am unsure. I see pluto well aspected for the most part in the comp. Saturn itself does not indicate abuse, however I see that you've outlined nessus. It is opposite the males venus, but that does not mean it will manifest. Yet the comp, indicates that it could because it is conjunct the dsc! Abusive partnership, be wary! Chiron and mars square pluto is scary also, this relationship does have a chance to turn to destructive tendencies.
Chiron on his north node and vertex is also a big one to indicate past hurts, and the healing of it. There is your karmic indicator, in the past life she could have hurt him and she wishes to heal it now. That is how he will move forward *north node indicates destiny and allows further development for the future* And these wounds will show up no matter what *Chiron conjunct Mars, opposite pluto*
All of this is veiled in the 12 house composite, and with saturn there, they will often wonder why they hurt each other and are yet unable to locate the true source of their misery *12th house symbolizes hidden things* and the 12th house also represents asylums, prison, monasteries, hospital. Saturn will make it very dreary and depressing opposing most of their planets, and they will be glued together until they figure it out.
Reads like misery to me. Best to leave this one alone. Even if he will *grow* (NN) it will also mean a lot of pain and suffering. Some things are better left in the past, especially since there are not enough positive factors here to indicate a functioning romantic relationship.