I also tend to side with CACycling's take on how it will go.

The extremely short length of this seat tube is putting a serious load on that upper weld. The setback post isn't helping either. Given all this it's hyper important to mark the ends of the crack with something to allow you to monitor the growth of this crack. You say you've been watching it for 3 months. But when something grows slowly our mind plays tricks on us. So marking the ends with a small permanent marker or paint is the only accurate way to track the growth of this crack.

If you find that it grows another mm or two over a few rides then the seat tube is in an active process of tearing away from the weld. If the crack lengths at all during use and with monitoring after each ride then once you notice definite growth that you can't say is a trick of your eye then it's time to stop riding this frame RIGHT THEN. Not later, right then. With each mm of growth in that crack there's more load put on the remaining metal. And that metal is already working at fatiguing. So it won't take much before the saddle suddenly folds back and down on you and into the rear wheel. While it won't snap off with a big CRACK! it will let you down in a rather dramatic way and likely cause you to crash. If this happens around traffic the resulting accident may be more than you bargained for.

Obviously suspensiom frames don't fit you all that well. For your next one may I suggest a regular double triangle non suspended frame? You'll get the cockpit spacing you want without needing to resort to oddball set back posts and at the same time you'll get a rigid frame that is accepted by most folks as being a lot more efficient to pedal thanks to no energy being sucked away by the suspension. If you really must have some extra cushion for your backside then go for a suspension seat post instead.