What to do when you feel stupid for liking someone?

I met this guy (Alex) through work. We have the same job & work together on the weekends. He is a senior in hs, & I am in my 1st year of college. We started out as "just friends" who hung out together after work on the weekends. He had recently gotten out of a long term relationship due to both of them cheating. Now, about 5 months later, we both like each other. The old girlfriend was never a problem, as he lost all feelings for her when she cheated on him. This girl that he cheated on her with though, is still around. She is obsessed with him. She goes over to his house without being invited, calls and texts him nonstop everyday (when he doesn't even answer because he's showed me messages) & she is a junior in hs, so they see each other at school. He treats me like his girlfriend, has told me that he likes me a lot, but still won't officially get rid of this other girl. He's flat out told me that he doesn't like her & that she's crazy, & he doesn't want her coming over. He then said that if me & him were to be dating, he would block her & not let her come over anymore. But we're not official, and I don't know why. He asked if I would date him if he was to ask, and I said yes. But he never asked, so I'm left reading her sappy tweets about him every single day, feeling stupid for still liking him. What's a good thing to tell him in this situation?
What to do when you feel stupid for liking someone?
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