Laxus dislikes weak people but what if you, as his lover are weak? He'd be troubled by that thought even before confessing to you. He might be madly in love with you but he has his worries and he doesn't want to lose you. He'd talk about his troubles with the Thunder legion and sort out the answer. The most reasonable choice would be that he's the protector you need to keep up with him. He'll be there whenever you are in trouble, he'd be your lovig partner but also a partner in any troublesome activity. He worries but also wants you to be confident of yourself and your magic. That's his answer. If you are weak, he'll be the stronger one you can lean on.