Hi my (22F) brother (26M) has gone through a rough breakup semi recently (5 months ago) and completely lost faith in the concept of relationships/love. It isn't like he can't meet new people or get dates: He is fit, has a high paying job and is overall intelligent and a good conversation partner. But his last breakup completely "broke him". When I asked him yesterday why he hasn't gone out to look for something new yet he was very open with me and he said he can't "put in the effort into dating/getting to know someone anymore knowing the relationship can end because of something absolutely out of your control."
Breakup background:
My brothers ex girlfriend (we'll call her Sarah) was together with him for 4 years, they bought a house together, were discussing marriage/kids for a while and were aligned on that. However when they shared it might "happen soon" one of the Sarahs friends "grew a conscience" and told my brother that for the past year or so she has been going out on secret dates with her old ex when my brother had evening plans with his work/friends. My brother confronted her about it and after initially denying she confessed she has been because "she was lacking pushback from time to time" (my brother and Sarah had basically no fights/arguments for the duration of their relationship as my brother was very "whatever's realistic and makes her happy is fine with me), by which she meant she missed having a passionate argument on disagreements from time to time and her ex used to give her that (note: she originally left her ex because one of these "heated debates" had gotten physical and he hit her). They decided to breakup, my brother couldn't see her the same way anymore after going from "I'm going to marry her" to what just happened.
My brother had 2 relationships before this which ended less dramatic (simply grew apart & a relationship that turned into LDR due to the past girlfriends work and they couldn't make it work due to timezones). But they never affected him like this. Me, my parents and our older brother are genuinely worried for him, he only goes outside for work/gym, barely speaks to his friends anymore (him and Sarah are part of the same friendgroups alot) and he is obviously less happy compared to months ago (and is getting worse) despite him reassuring us that he's fine.
Is there anything we can do/say to convince him to go out and meet someone new again? I know it shouldn't be my business but he is very obviously less excited about life for months now and I'm worried for what might happen. I've suggested datingapps but he told me that he has a huge dislike over something so superficial and called it "a meat market". Then I said he should go out clubbing with his friends again where he said he never looked to meet proper relationship material while clubbing and that he's sure he won't find anybody there, on top of saying he's too old to do that. I'm at the end of my rope here but I just want my cheerful brother back to be honest.
Tldr; brothers ex cheated and brother found out. Lost all faith in every being with another woman again even months after