I'm 34 yrs old and three weeks ago I found out I was thirteen weeks pregnant.
The baby that you lost at 21 weeks is still having a big impact on you. It must have been a very difficult experience for you to lose a baby so late in the pregnancy. I wonder if an abortion would feel like another big loss and that is why you are struggling with this decision.
Your relationship would be difficult if you kept something like this secret, but you also don't want to be pressurised into an abortion before you are sure about it. Although you are 13 weeks I think it's important to be sure before you make your decision, so that you don't regret it afterwards.
Maybe it would help to speak to someone independently who can help you think through your decision. You can ring the national helpline 0800 0282228 and talk to a trained advisor.