Do you genuinely not believe they're happy together, or do you simply not want them to be happy together? Jealousy is a powerful and very corrupting thing.
All I can say is, get over it. Sounds harsh but such is life. Hannah is entitled to run to her bf before running to you, because in any healthy relationships, you're meant to be good friends or best friends with your partner in the first place. In fact, even if he wasn't her bf, Hannah is entitled to run to whomever she wants for advice. Just cus she doesn't come to you anymore does not mean she is not grateful for your help in the past, and it does not mean she's not your friend or "less" of a friend to you.
I mean, to be honest, how should I feel by now if I get jealous like that? And I do sometimes. Every good friend of mine - and I try and be there for all of them whenever they need me, I'd sit there for hours listening to them if they needed it - but every single one of them met other friends through me, and as time goes by suddenly they're not as close to me anymore and they prefer the company of the other girl. You just get over it - you don't own your friends and they're entitled to be closer to other people other than you. But just cus they're closer to other people does not mean you're not still their close friend and it does not mean they don't need your friendship anymore.
When you feel the jealousy rising, just tell yourself to stop. It'll go away as time goes by.