They are almost same, but with different tenses. Sev-er; its in aorist form. (this is what we call "Geniş zaman". "Aorist form" denotes "continuing activity". Sever; he/she/it continuing to 'love' in this word. Sev-iyor; is used in the "present continuous" tense in this word.

At first you can think "geniş zaman" (sev-er, gel-ir, koş-ar etc.) as simple present tense and "şimdiki zaman" as present continuous tense (sev-iyor, gel-iyor, koş-uyor). This explanation enough, just for now.

Ops,,, İ typed it wrong, it's (seviyorlar)

I didn't understand what do you mean by 'savıyorlar', if you write it in English, I can help.