Quoting godlovesugly ♥:" Well my SO thinks he has it. He had it really bad last year supposedly and he said last time his doctor said no physical or sexual contact for 2-3 weeks. Wtf?"
Most of the time it's bacterial. Unless they thought it was caused by something that's sexual transmitted, then there shouldn't be a problem. I know there's a few STD's that can hang out in your throat like gonorrhea and HPV but they'd have to actually test for them. I guess the bacteria can transfer to you if he goes down on you and cause some kind of bacterial infection.
ETA: A few months back, I started to get pain on my one tonsil. I looked at it and there was a sore on it. It was small. My OB tested for whatever STD's can form in the throat but they came up negative. On Wednesday I went to my doctor for it because it's pretty big, white and hard. I also have a horrible ear infection. Turned out it's a tonsil stone and it caused an ear infection.