My boyfriend has testicular pain from time to time? Is it my fault?

Unlikely. It is his testicle and unless you purposely injured it is not likely to be your fault. Normal intercourse does not cause testicular pain. However, prolonged erection causes vascular congestion in the groin in general, including in the testes and may leave an ache in the testes. Other causes of episodic testicular pain may be varicose veins and inflammation.