How do I let go & not care.

currently dealing with is with someone whom I knew it would never work out with. We are from different worlds & our family/groups basically hate each other. He lives with his very toxic ex who is ultimate drama & control. we have been seeing each other on the DL for 5 months. I was at the tail end of a different set of heart aches & was just looking to have fun with someone to ease my mind. What started off as just a "fling" (literally after one night) turned into him just being prince charming (excluding us hiding it from everyone) letting me know how amazing I am & changing the way he felt about life. I tried to put things on ice by saying we should just be friends because of our situation but he insisted he liked me more than anyone he's met in years. We have talked everyday of the last 5 months with a time or two of the ex trying to get involved but never know what was up or who I was. I know this is all read flag stuff but emotions right. well 4 days ago he started saying that he felt in love with me, I'm basically the best that's happened to him & sending me love songs.