About my builddd.
 

Well, right now I'm a lv 25 cleric, with a 1:1END:SPR ratio. I can tank pretty well for a lot of things, actually, but killing can take some time without more DPS help. I mean lately, up to lv 25, I rarely did not party. I'd always have friends to ask "Hey! Do you wanna go to mt? bh? etc." And in cb2, my build was 1:2END:SPR and I did perfectly fine up to 27 because again, I'd always have someone to party with. But sometimes I think I rely too much on parties, so was wondering if I should add STR now or continue with my build and just wear STR rings or something.

No, just keep in parties. They're damn easy to find right now, especially for clerics. If you enjoy your build, stick with it. I would suggest using STR rings due to your high SPR anyways, as it would effect your damage more due to the amount of crits you hit.

agree with the above posters. you will have no problems finding a party. and if it should happen sometimes, putting some points into str for only these occasions is a complete waste.
if you are in a party - even if its a duo - and you are attacking as well, your dmg will still be the lowest and a few more points wont make any difference in your killing speed at all
but later on when you will be needed to keep a party alive, in pve or pvp, you will HAVE to survive. noone will ask you how much dmg you can do in pvp agains one of the 4-5 mages and fighters bashing on your partymates. youl will be expected to keep your party's HP up and to stay alive yourself as well. now in these situations str will be useless to you.
it does help you solo for sure, and if you are going to solo/fight a lot then it will be important. but in you wont, you can spend your points on more useful attributes

- Agrees with everyone else -

Stick to parties! xD I'm using that 1:2 END:SPR build at the moment. I'm planning to start adding STR after I cap SPR at 25, so maybe you can try that too! I don't think us clerics need that much SPR points since we get more SP from our Divinity skill as well.