Hi, I'm looking for some practical, no nonsense advice. I've always got great feedback on here 
I am 23 years old (next week) and I have been living with my boyfriend for 4 years this September (he is 27).
We recently bought a house together and share the majority of our possessions. We have a dog, a cat and two rabbits.
I love him very much and he loves me.
He is kind, thoughtful and very caring and we both see a future together.
I feel very secure in our relationship and trust him deeply. I've always had very bad relationships with men (my father and step father were both abusive) so hadn't experienced a stable relationship with male figure up until OH. I also used to self harm excessively and have an instable personality (very high, very low) which has calmed down significantly since I've been in this relationship. (I no longer self harm). My best friend thinks he is a very good influence.
However, throughout our whole relationship I've always wondered what it'd be like to not be in the relationship. This has risen and fallen from simple "what ifs" to down right fantasies.
We also have pretty different aspirations/ambitions. OH is a very hardworker and puts 100% into everything however I know that he would be happy working in a low grade job for the rest of his life, he doesn't really have any career aspirations. (He is not lazy though). His currently salary is about £16,000
I however have big ambitions, just nowhere to put them. I jump from idea to idea and don't really have any long term interests or hobbies. I'm a very flash in the pan person. Having said that, I have built myself a fairly solid career in both admin and nannying and either one would bring me £25-£30k a year (I'm currently on a nanny run).
I am comfortable with him intimately but dislike extended periods of physical contact. Our sex life has significantly dimished over the years but is still what I'd describe as healthy.
I would live a very different life in my 20s if I was single.
I know that if I wasn't with him I would feel quite rudderless.
I'm frightened of staying with him and missing out on being single and "free". I'm frightened of staying and then breaking up later on in life because we are not perfect and having missed out on life. I'm frightened of staying and resenting him - which he does not deserve.
I'm frightened of leaving in case we are good together and I'm just having a grass is greener outlook. I'm frightened of leaving and having nothing.
Any advice is appreciated. My apologies for the essay!!!