This is such a heavy thing to carry, and I really feel for you. Honestly, the drop in intimacy can sometimes come from stress, health issues, or even just age-related changes in men, so it does not automatically point to cheating. But I think the most important step right now is to have an honest, calm conversation with him, maybe even suggest seeing a couples counsellor together, because these things really do need to be talked through properly. You deserve to feel secure and loved in your marriage, so do not just let it sit and fester lah.