You can have a relationship. Just remember not everyone is as strong as you are mentally and emotionally after overcoming the many challenges you have encountered regarding your health since birth. So, hang in there.
You should encourage your partner to learn about Tetralogy of Fallot, ask your partner to join you at your heart appointments, and be patient with your partner as they do their best.
If you are comfortable with yourself, your partner will be too. Just take your time like everyone else in a relationship.