What do I do about him?

My 2nd bestfriends boyfriend is one of my best friends. we have been friends for about a year. Him and Her went through a rough spot and they temporaretly seperated and he leaned on my lke a crutch he. acted like I was only for him to talk to...and it felt good. I now am in it deep for him. he texts me literally everyday around the same time. he and my bestfriend have been seperated for about 2 months now and he tlkas to me all the time still. But, my other friend, is a complete and total slut. I am recently not friends with her anymore. The other day he told me that He had a crush on her because he thought she was cute. I was hurt to say the least. I told him about her ways and he backed off.... thanking me for telling him... I don't know why I love someone that unknowingly puts me though so much emotional pain. it doesn't make any sense to me at all... He told me he loved me in a "friend" way out of the blue one time and I felt like air. I loved that feeling. and he wants to hang out al the time to. I told my bestfriend that He was killing me. she told me that if he didn't love me for me he wasn't worth it. She believes I should tell him...but...I don't want to....I'm to scared....any advice?