Is it normal to have side feelings when already in a relation ?

ive been in a serious relation with my bf for the past four years and we are looking forward to marriage in the coming four to five years .... He is a very loving decent person and extremely faithful .... The problem is that faithfullness doesnt come so easy from my side, i have to make efforts to remain emotionally committed ... The problem is that he isnt very attractive and is too decently boring, me on the other hand tend to attract a lot of guys, we become friends, text or chat sometimes and they easily start falling for me, as in i dont meet them and all, am kinda reserved in person but they sometimes look upto me when they are sad or lonely, i act friendly and they start saying ''i love you'' within a few months of knowing me and there comes the end of our friendship ... The thing is even i tend to get emotionally attached when our friendship has been a long one, i feel love and affection for them but have to subdue such feelings and just let go of my temporary infatuation ... It has happened about four or five times in the past two years and ive really begun to doubt mt integrity as a person now... I feel like a player for making them fall for me but at the end of it all, i confess to my guy, he takes me back and i suffer days of killing guilt ...i wish it would not happen ever ... Easily