Would it be worth the time and money to fight for visitation with my son?

I do have parental resposibility but my son’s mum has stopped me from seein’ him for her own strange reasons.. I used to have him every other weekend and also had to travel to Preston from Manchester and back again and once again takin’ him home, I also provide cash for what ever his mum says he requires.. Now she’s met a new fella and it seems that mine and my son’s relationship don’t matter.. Do I even stand a chance goin’ thru the courts because this is killin’ me, it’s been 3 months since I last saw him…