Sister told me about her non-Muslim boyfriend

Assalamu alaykum,

I come from a first-generation immigrant family from the Middle East and have been living in the UK for slightly less than 10 years. Recently my sister (26F) told me that she has had a local non-Muslim boyfriend for the past 8 months.

For some background, my family and I have been trying to find her a good husband prospect but haven’t been successful. My family doesn’t really know about her boyfriend, and I only found out yesterday myself, as we live in different cities. My family is quite closed-minded and conservative about many things, especially culture and religion, so she has only told me and asked me not to tell them.

She is practising, though I do have suspicions that she might not be keeping up with her daily prayers (may Allah help her). She told me she has made clear to the guy that marriage would be impossible unless he becomes Muslim, and that he is now learning about Islam. I have concerns about how sincere this is (though I know it isn’t my place to judge), partly because my sister herself is quite weak in terms of religious knowledge. I haven’t met him, and only know his name and profession from what she’s told me.

I love my sister and wish nothing but the best for her, but I don’t know how to approach this. I don’t want her to lose her deen and her identity. Could anyone point me in the right direction?

Jazakum Allahu khayran