Re: what if
Multiple realities is the only way to answer the question. He creates a new and similar reality in which his loved one survives.He has no memory of the events as they didn't happen in his past. Why he wouldn't meet his past self is well glossed over in the story. The fact is, with each failure our hero would need to go back further and further to avoid his other selves. Alternatively he could gang up with them and form a wall in front of the carriage.
Sadly, they both seem incredibly inept at keeping our heroine safe, I fear the Universe won't have to wait long for the seperate realities to merge again as she falls out of a window or slips under a train or some other bizarre fatal occurence.
The paradox arguement is based on an over inflated belief that our actions really matter or make any difference. The question is does the Universe really care if we go back and kill our ancestorrs, the answer is most likely a resounding no..