Scared of leaving longterm relationship

I am 37, female and have been with my partner (39) since I was 18. In hindsight we rushed into our relationship and have stuck together through a great deal. We are not married and have no children. He has helped me through illness and personal problems (I was abused as a kid). He has been amazingly kind and generous and I love him dearly, but am not 'in love' with him. He has if I'm honest been more of an emotional crutch and more like a trusted and wonderful best friend. I feel terrible about this but for the past three months I have become involved with and fallen in love with somebody else who I feel all the physical/emotional passion for that is lacking with my partner. My partner now knows about this and we have mutually decided to take a break from one another, he has been remarkably calm about this actually. I guess I have reached a kind of crossroads, I have been thinking a great deal about how you only live once and how I don't want to go though life having never felt this overwhelming emotional/physical passion I feel for new guy. I have never wanted children with my partner, but would consider it with this new guy who I adore. I know this sounds selfish, but I am frightened of leaving the security, routine and I guess comfort of my relationship. I will miss him like crazy but again am not 'in love' with him. I am also scared of my families reaction who love my partner who is part of the family. I do want to be with this new guy, I have never felt this way about someone before. Any advice is welcome, I will add I have never cheated before and wouldn't have were it not for this other guy, I know this odes not justify my actions.

No one will be able to tell you what you should or shouldn't do at this stage. And I am going to say this, and you will say ''no no this is different''.... But everyone feels like that with a new partner. He has excited you and he is new and interesting, and it makes you get that passionate nervous love back. But it will not last. I did not last with your partner, and it will not last with the new guy. The question you should ask yourself...do you want to give up someone you care deeply about, who has reliably been there for you...through thick and thin for a few months of passionate sex?