Am I sinning simply by feeling jealous about my spouse?

Feeling jealous is not in itself a sin; it is a natural feeling, and what is judged is how you act on it. Even the wives of the Prophet ﷺ felt it, and he once said of 'Aisyah's jealousy: “Your mother is jealous” (Sahih al-Bukhari 5225), without condemning it as a feeling. What becomes wrong is when jealousy leads to accusations without evidence, control, injustice or cutting family ties. So acknowledge the feeling, then manage it fairly and calmly. Let it motivate you to care for the relationship, not become an excuse for wrongdoing. A feeling managed with taqwa will not bring sin. See relationship psychology.