Does changing shuls have to be one of those, *WHAM, BAM, & GOODBYE* kind of deals?
Maybe it’s just me, but why can’t you taper off of one shul? Perhaps you already tapered off and are spending more time at another shul.
Sometimes not saying anything leaves it open for you to also go back, once in a while, if you want. Maybe you want to stop by and shake the Lulav and Etrog there, just to wish the rabbi and community a chag samayach too.
It doesn’t have to be all or nothing, you know? When it comes to what to say, you can make it simple and vague. You had other things going on at this shul. You love both places, but clearly you need to be someplace else now. People, especially a rabbi that you were close to, ought to understand and wish you the best 🙂