Prey　fear　and　gregarious　behavior　form　a　bidirectional　feedback　loop　critical　to　ecosystem　stability.　We　quantify　this　bidirectional　feedback　by　using　GSE　mechanisms　and　extending　this　framework　to　seasonal　environments.　Mathematical　analysis　and　numerical　simulations　validate　the　proposed　model.　Research　shows　that　increasing　fear　intensity　eliminates　positive　equilibria　via　saddle–node　bifurcation,　while　GSE　mitigates　this　by　enhancing　group　survival.　Under　bistability,　the　number,　spatial　distribution,　and　stability　of　interior　equilibria　exhibit　selective　dependence　on　both　fear　parameter　and　GSE.　Fear　and　GSE　form　a　feedback　loop　that　can　stabilize　ecosystems　or　trigger　extinction　via　bistability.　Notably,　fear　effects　and　GSE　exert　opposing　influences　on　model　dynamics.　Furthermore,　it　is　highlighted　that　seasonal　variations　modulate　but　do　not　fundamentally　alter　the　underlying　stability　structure　dictated　by　fear　and　group　size　effect.　Seasonal　forcing　amplifies　these　dynamics,　with　prey　initial　density　being　critical　to　persistence.　This　study　establishes　the　first　theoretical　framework　unifying　GSE-driven　fear　feedbacks　and　seasonal　forcing,　offering　mechanistic　insights　into　ecosystem　resilience　and　extinction　thresholds.　©　2025　Elsevier　Ltd