Yes, it does sound like he’s feeling insecure. The best thing you can do is to sit down with him and have an open, heartfelt conversation, let him know how much you care and reassure him of your faithfulness. Sometimes a little honest communication is enough to ease those doubts. But if you’ve tried that and he still refuses to trust you, then it may be time to be very clear: either he works on building that trust, or the relationship won’t be able to move forward. The foundation of a relationship is trust.