So afraid to open up again

My boyfriend and I broke up we had been. Together for three years we had a very loving relationship but at times he struggled a lot with being able to provide a mutually satisfying relationship . He gets too close to me and would pull away and after three years of trying to show him I'm here to stay I couldn't do it anymore . Now that men have been approaching me to go on dates and things I have no desire I still long for my ex no matter how hard I try to get over it and he's already on a relationship a month after we broke up but I have no desire to date or be with anyone in fact i feel super terrified and I don't know what to do . Help ?