You ground me (The Martens brothers #6) By Marianna N

I love this series. And I really love that it's moved on to the next generation with JJ...
He and Heather have kind of grown up alongside each other with their families being so close, but he was always a few years older than her and they saw each other as 'sort of' cousins... but just before he was about to leave for Japan he kind of noticed that she wasn't such a kid anymore. Hello! She'd changed from a child to a woman while he wasn't looking.
Fast forward three years or so and she's changed even more - but now she's in an abusive relationship and JJ is desperate to save her... All the fun, angst and drama you've come to expect from Marianna... Brilliant. Loved it. You ground me (The Martens brothers #6)

I haven't seen her in three years and I never thought I will be this protective over her again.

I haven't seen him in three years. I went crazy when he left and I will get him when he comes back.

Love will win over everything.

Three years they haven't seen each other and when JJ comes back from Tokyo, heather needs his help even she doesn't want help.

Heather is the troubled girl, and JJ is the guy who will ground her. You ground me (The Martens brothers #6)