Need some advices

[the real god emperor]

I am a 2h cavalry.And imo i am pretty good at it, but ranged could be a problem most of the time, when i am nearly backstabbing them, they turn around and shoot me, pretty annoying. And my build is not complete yet, so i can put some skills on shield or athletics to fight on ground. What do you think guys? should i have a shield with my morningstar?

[Bifi]

A shield on your back won't help you that much.
If you think about using your morningstar with shield, you gonna have a problem since it takes 1h wpf if you use it with a shield.
Of course you can always swap out your shield, but that's a kinda bad solution for your archer problem.

I think you would be better off, if you invest in athletics and carry around a 0 skill shield.

[Ronin]

Can you post your build and current level kratos? That changes things I think. Also what equipment you mostly prefer is also important. You indeed might need a shield if you are riding a plated charger with 5 riding, but 8 riding with an arabian might be sufficient to dodge arrows if you see what I mean

[the real god emperor]

Level 25 16/18 will be 21/18 at the end. 6 riding 5 wm 5 ps 0 athletics atm, got 2 skill points to use. only 2h wpf, having a might morningstar my own, and a champ destrier from the armoury, so horse might change.

[Ronin]

Hmm how about making a 18/18 character with more ironflesh and more athletics. I personally use 18/18 as a cavalry (1h) and do enough damage. Since you are using a 2hander, the damage should be fine. Besides I think you are really going to need some ironflesh as a 2hander. And twohander cav can also be a very good fighter on foot (with the athletics). I don't think weapon master is that useful on horseback by the way, so you will get the best benefit when you're on foot I think.
All in all yuou would be a better judge of what you need though.