When a man wears a condom , the glans penis where sensation is felt most is covered. So it is possible that when your boyfriend wheres a condom he knows that he wont be having any pleasure, and therefore he loses interest in the act of sexual intercourse.

If its STD's your worried about , BUT if you TRUST your boyfriend , you can go on the pill.

Before you even think of taking Viagra I suggest you talk to a doctor.

The main thing is talking about it together and asking about how he feels about it and what you can do to increase his pleasure during the act of sex.

Which might make him exited into having an erection.

Male erectile dysfunction is mostly psychological disorder.