If I have only had 1 sex partner

and they have only been with me and never cheated on me

can we still give eachother stds if we are unsafe and maybe havent takin a shower or something?

He is the only one I have slept with and im the only girl for the past 3 years he has slept with, but has had other partenrs b4 me. I do not think or I am not sure if he has cheated on me.

Could he have been infected before and still doesnt know it???

If I didnt know until now could I have reinfected or worsened my std???