Hello all, I just wanted to come on here and share a few things that have helped me to stay motivated. 
The first, which I have mentioned before, is that struggling with M, while dating or engaged, would not be ideal for anyone involved. Secondly, remembering how awful I felt, after having a fall, is a form of discouragement that I find useful. Another way, is to read the daily boosts, which, provides chizuk and encouragement. 
One crucial part, is to eliminate any impure thoughts from your mind. When you are fantasizing about dirty things, it keeps you from freeing yourself of the urge to fall. When you remove those thoughts from your mind it becomes easier to stay clean. 
Lastly, having a partner who can keep you accountable provides tremendous motivation to stay clean, by not only keeping you accountable when you have a fall, but you can share your thoughts and struggles and help each other out. 
Wishing everyone much hatzlacha!