Why do all married men hit on me what are they upto

Hi guys im a 21yr old pretty looking girl,I goto a medical school..my problem is that all the married staff members try to hit on me..one of my staff memeber is around 34yrs of age,married and has a daughter..he was always good to me,supported me,cared for me and my emotions,gave me the best marks…and also offered me a job..I used to think that he is a dignified man because I knew him as a staff from 3yrs..he never tried to get physical or something but as soon as I started working with him he began to flirt with me..he used to tell you are sooo beautiful any guy would fall for you,you are very naive…he was always interested to know who all tried to hit on me..I trusted him so much,I shared all my personal problems with him…recently I went for a month vacation and I saw a change in his attitude he isnt coming to job regularly…earlier he used to come almost everyday just to meet me,drop me home..in a way even I was infatuated by him..but the other day one of my friend told me that he is just using me to get his workdone..I asked him directly ..he said nooo,its not like that trust me..I would love to spend time with you its just that people are spreading rumors,people are thinking that im spending too much of time with you.please tell me what is he up2