noone can answer this but you .
there could be many reasons given , however only you would know the true answer.
suggestions
you may think you dont want to fail ,
you dont want to hurt him ,
enjoying your own company and actualy being alone are two different things , so you could fear loneliness itself " not being alone but feeling alone ".
financial concerns
you may actualy love him and are just going through a bad patch.
seeing his faults , but realise you have them to so are unwilling yet to act.
just a few suggestions but to be honest as stated only you know why , you want to stay with this man " or not want to split with this man ".