You don't need to complete the rebel chain to marry him at the end. To avoid getting dump for any guy is to have high enough romance with them so that if they try to break up you have all the right answers to avoid a (permanent breakup) where instead the romantic option needs to think and comes begging back.
To increase romance you either have to pick the dialogues with the highest amount of romance or go on more dates with your intended ( I noticed two dates are enough )
fyi: if your romance is very high, the break-up (attempt) won't even happen. That was the case with me in my second walkthrough with Clarmont.