The thing is with kids, teenagers, young adults...the gestures don't matter. Cookies, treats, etc., are not what matters. What matters is the day to day ups and downs, the being there for them. Getting fed up together, having upsets, putting them right, enjoying a laugh. Just the day to day stuff that we all have.
My ex made it clear that he wasn't leaving his kids, just me. Well, clearly that wasn't the case. He would go weeks and weeks without contact, because he was tied up with OW (and her kids, who he prioritised over his own). Then, he would suddenly decide to sweep in and offer them a meal out, or buy them something. Then, he would sulk when ignored, and they didn't fall over him. Because, and this is key, especially with teens, they work it out for themselves. I would get so irritated when he did take them out for a treat, and I was left, hard up and struggling to feed them all, to deal with the moods and usual teenage angst. It seemed to me that he got the good stuff, and I got all the dross. Well, if any of you identify with this, let me tell you that with hindsight - I was wrong: Yes, I got all the ups and downs BUT the bond that grew from being the stable, reliable one, was priceless.
What happened then (for me) was that ex decided that the only reason he didn't have the bond with his kids, was me. I turned them against him. He couldn't then, and wouldn't despite them telling him, accept that he did that, all by himself.
So I suppose my point is that if you now feel that it isn't fair, because you have to deal with a break up and suddenly raising kids on your own, remember that in the future your kids will always know who had their back when it mattered, and will never let you forget it.
We could have split up and he could have called them, seen them, every day, but he choose not too. He did that. Then, when he occasionally surfaced from his love bubble with ow and remembered them, he wanted to dip in and out without putting himself out. What he still doesn't get (or can't allow himself to accept) is that he made the choice to prioritise himself, his immediate wants and needs (OW) over the mundane of being a hands-on dad.