My girlfriend and I have been going strong for over a year now and we are in a really good spot right now. GF gets a train to uni everyday and she is normally accompanied by one of my friends (let's call him Frank). Frank is someone that can be quite narcissistic at times and says whatever is on his mind before thinking. Today I found out he offered to share rooms with my GF as they both attend nearby unis. I feel quite jealous about it and I can't stop thinking why it would be okay for him to just casually ask my GF to move in with him. Frank has never been particularly successful in relationships and he has tried to get together with my exes on a couple of occasions. AITA? Or is there cause for concern? 

TL:DR Old friend of mine asks my girlfriend to move in with him, am I right to be jealous about it?