He broke out of the friend zone

Sierra • due June 2019 💕💕
So about a month ago I started officially dating my best friend (of 13 years)  which is great I love him dearly but here's my problem... things have been getting heated lately but I pull away before anything happens. I think I'm scared to move to the next level with him because I can't stand the thought of things going south and losing him completely. 
I'd really like some advice on where to go from here am I just being paranoid and everything's going to be fine or are there reasonable concerns?