Remus and Tonk's marriage was rushed and unexpected and the fact they had a baby was even more of a rush. I really did not expect Remus to marry Tonks as he did not think he was able to provide for a wife etc. But I think it was a one sided relationship in that only Tonks was in love with Remus and Remus did not really love Tonks. Their death was even more of unexpected and JKR did not really go into how they died.