Well, to keep from tearing them, slow stretching is the best way. And thats just added foreplay

As for the problem you have reaching climax... That one would be you yourself. Either it is a problem you have within your psyche, or one that you have emotionally.
Are you comfortable emotionally with the partners you've had/have?
Are you afraid of causing them pain/hurting them?
Do you ponder that when engaged in sexual acts?
The last two connected questions can have a lot to do with the end results..