I think for most couples (not all) a lack of sex altogether, will be the breaking point. It’s a question of how long it takes for the person who is unhappy with the situation to appreciate how much of an impact it has for them and decide to leave. Incredibly painful.
I’d say, you shouldn’t suffer in silence and although it’s difficult to address it with DH, it’s vital to do this. There could be all kinds of possible reasons...medical, including depression or other factors. Only when you talk about them (and possibly go for some kind of counselling or therapy) can you start to see if there might be a way forward. Sometimes they won’t be, but I think most people really would like to explore the options to bring about change, if it’s that which will save the marriage.
The longer people leave it, without talking about it, the deeper the separation between the 2 people can be and the harder to restore the relationship. It can reach the point if no return, even if there is action that might help.
It is really hard when there are children, as leaving is for most reasons. However, don’t just see sex as a ‘nice to have’ in your relationship and something you should be able to live without. It’s much more than that for the vast majority of people. You might need to think about if you can address it and see if there’s a way forward, or think seriously about the future. It wouldn’t be unreasonable or something which was selfish, but totally to be expected, especially if you have explored all the options of moving forward and finding resolutions. Some people do find a way forward with this, often through some kind of counselling, or even just throug open communication between themselves....but longer term sexlessness doesn’t normally resolve itself without anyone being willing to speak about it. Incredibly hard.