It is a noun/na-adjective and means “be obsessed with”. It is used when you think about someone/something all the time. “ハマる” is a verb and it is commonly used in spoken or informal language.
Ken has been really into online games since his mother took away his video games.
母親にビデオゲームを取り上げられてから、ケンはオンラインゲームにハマっている(or夢中だ)。
母親にビデオゲームを取り上げられてから、ケンはオンラインゲームにハマっている(or夢中だ)。
- Amy : Do you want to go get some drinks after work?
仕事が終わったら、飲みに行かない？ - Meg : Great. Why don’t we ask Kumi?
いいね。クミも誘おうか？ - Amy : I’ve already talked to her, but she is going out with Taro.
もう声をかけてみたんだけど、タロウとデートだって。 - Meg : Again? I think she is seeing him all the time. She is obsessed with him.
また？いつもデートしているね。彼に夢中だ(orハマっている)ね。 - Amy : What would you like to eat for dinner?
今夜、何食べようか？ - Meg : Anything is fine. You choose.
何でもいいよ。決めて。 - Amy : Let’s go to eat Ramen! I’m hooked on Tonkotsu ramen.
ラーメンを食べに行こうよ！豚骨ラーメンにハマっている(or夢中な)の。