If you have broken your girlfriend's heart and want to make her happy again, it is important to approach the situation with genuine remorse and a willingness to make amends. Here are some steps you can take to rebuild trust and bring happiness back into the relationship:

1. Apologize sincerely: Start by acknowledging your mistakes and taking responsibility for your actions. Apologize to your girlfriend genuinely and without making excuses. Make sure she knows that you understand the pain you caused her.

2. Show empathy and listen: Give your girlfriend the space to express her emotions and allow her to openly communicate how she feels. Practice active listening by validating her feelings and showing understanding. Avoid interrupting or getting defensive.

3. Demonstrate change: Actions speak louder than words. Show your girlfriend that you have learned from your mistakes and are committed to making positive changes. This may involve addressing the specific issue that caused the heartbreak and taking steps to ensure it doesn't happen again.

4. Be patient: Rebuilding trust takes time and patience. Understand that your girlfriend may need time to heal and may initially be hesitant to trust you again. Respect her boundaries and give her the time she needs while consistently demonstrating your commitment to change.

5. Rebuild communication: Open and honest communication is crucial in any relationship. Make sure you establish a safe space where both of you can openly express your thoughts and emotions. Encourage transparency and actively work on improving your communication skills.

6. Show affection and appreciation: Small gestures can go a long way in showing your girlfriend that you care about her happiness. Surprise her with thoughtful acts of kindness, express your love and appreciation for her, and make an effort to prioritize quality time together.

7. Seek professional help if needed: Depending on the severity of the situation, it may be beneficial to seek couples counseling or therapy. A professional can provide guidance, facilitate healthy communication, and assist in the healing process.

Remember, rebuilding a broken heart takes time, effort, and consistency. It is important to be understanding and committed to making positive changes in order to regain trust and bring happiness back into the relationship.