The core of the sentence is:
The entire middle part 「積み上げるのに苦労して、失う時が一瞬なんて」 just adds more information to the core. It would not change the basic meaning of the sentence one bit.
So, let us examine the core now. Notice that ほど is paired up with ない. The core says:
"There is no 投資 as 割の合わない as 信用."
= "There is no investment as not-worth-the-candle as trust."
In other words, it is saying that trust can be really rip-offy. But why, you wonder. That is where the middle part comes in telling us how it can be so rip-offy.
"(as/because) one struggles much to build up (trust) yet one can lose it in a flash"
I hope I don't have to combine the two parts into one English sentence. I shall leave it to you as it is your language, not mine.