(Posting for a friend who shared this with me, not knowing what to do)

He has struggled with P&M since high school but really started taking this nisayon seriously after spending the year learning in Israel. B”H over the last 5 years he has seen a lot of progress. As time went on his streaks got longer and although still struggling he B”H was really improving. He said for the most part if he was really frustrated or anxious that’s when the struggle would come. Any time he was busy and his devices were filtered he was in a good place. He says he thinks that the main aspect of his struggle was rooted in trauma from the loss of a close relative around three years ago. Although he doesn’t feel he was ever addicted he still never truly felt out of the woods. He wasn’t sure when he should start dating but after speaking  to some friends and Rebbiem he felt like he was in a good place to start. He begin dating I was really motivated to stay clean and B”H did. He B”H got engaged to one of the first girl he went out with. After being clean for close to six months and newly engaged he fell. He came to me really distraught asking advice. He really feels terrible and is not sure what to do. Should he see how he bounces back before speaking to a anyone?Should he share this with his kallah? He mentioned that although feeling awful, he is very motivated and will continue to work hard at this challenge. I’ll be totally honest I really didn’t know how to advise him and was hoping the chevreh would have some good eytzuh. 

Tizcu Lemitzvot!

He should stop hiding behind you 

This may be a serious question requiring expert advice, but maybe it is just typical chatas neurim, except much less often than most bochrim? If it is only masturbation I don't see why to tell his kalla, especially if it is mamash once in a while. Curious what the oilam thinks. Of course, tell him to join gye himself...

My thought are that he should speak to an expert ASAP before making any big mistakes, and before getting married!
He should be completely honest with the person he will be talking to, Having one or two sessions with a professional therapist about the truma can also be a good idea (he probably doesn't need serious therapy, but you never know)).
It's also important for him to be open & honest with his chosson teacher.
​And of course joining GYE is recommended as well 
May we only hear good news and simchos!

P.S. Wait around for a while to hear more from experts here before addressing your friend, and btw its very kind of you doing this for him, you are a real good friend, he needs you a lot as well. 

First of all, follow Foolie's advise and send him here or to speak to someone. Second of all, no way should he tell his kallah. I don't see any reason that this fall is more serious than any slips. They happen. We have to do whatever we can to ensure that they don't happen, but when they do the world does not end. Just as he picked himself up from all the falls in the past, he's should move on and not obsess. Yesm he was hoping that the YH had retired, but that didn't happen. And it isn't going to happen until the day Hashem shechts him. So, tell him to continue all the wonderful work that he's been doing until now. And reach out to someone that can help him.

To be honest, I had the same issues, including what transpired before engagement. It sounds like your friend is very embarrassed and ashamed both of his abuse and use of P and M. He is hiding it even from us... Abuse is not something you can hide from. I also thought I was done with P and look were I am. He should speak to his Chosson Rebbi if he has a competent one, and know that he has nothing to be ashamed of and all to lose if he doesn't. I understand his struggle as I never told mine, but I wish I had, it would have saved years of suffering. MH