It sounds like you both have a good friendship and you won’t lose her unless maybe if you get angry at her and start a fight with her about her not telling you about her boyfriend sooner.

Why didn’t you ever tell her you had feelings for her? Are you very shy?

Moving forward, you can consider her a friend, same as always, but not a girlfriend. Maybe she will break up with her boyfriend sometime and you will tell her you’d like to take her out on a date.

But also start working on meeting new women and combating that shyness.