Example Visualforce page that shows Opportunities with or without Contact Roles.

SampleOpportunityController.java

public with sharing class SampleOpptyController {

    public List<Opportunity> opportunities { get; set; }
    
    public SampleOpptyController() {
        this.opportunities = queryOpportunities();
    }
    
    private List<Opportunity> queryOpportunities() {
        return [
            SELECT
            	id,            	
            	name,
            	stageName,
            	closeDate,
            	(
                    SELECT
                    	id,
                    	contactId,
                    	contact.firstName,
                    	contact.lastName,
                    	isPrimary,
                    	role
                    FROM
                    	OpportunityContactRoles
                    ORDER BY
                    	isPrimary,
                    	contact.name
                )
           	FROM
            	Opportunity
            ORDER BY
            	closeDate DESC
        ];
    }
    
}

SampleOpportunityPage.html

<apex:page controller="SampleOpptyController">
    
    <apex:sectionHeader title="Opportunities with or without Contact Roles"/>
    
    <apex:repeat var="oppty" value="{!opportunities}">
        
        <apex:pageBlock title="{!oppty.name}">
        
            <apex:pageBlockSection columns="2">
                <apex:outputField value="{!oppty.stageName}"/>
                <apex:outputField value="{!oppty.closeDate}"/>
            </apex:pageBlockSection>

            <apex:pageBlockSection columns="1">
            
                <apex:repeat var="contactRole" value="{!oppty.opportunityContactRoles}">
                
                   	<apex:pageBlock title="{!contactRole.contact.firstName + ' ' + contactRole.contact.lastName}">
                    
                        <apex:pageBlockSection columns="2">
                            <apex:outputField value="{!contactRole.isPrimary}"/>
                            <apex:outputField value="{!contactRole.role}"/>
                        </apex:pageBlockSection>
                    
                    </apex:pageBlock>
                
                </apex:repeat>
            
            </apex:pageBlockSection>
            
        </apex:pageBlock>
        
    </apex:repeat>
    
</apex:page>