We do not control our feelings. Unless we have skills at applying cognitive-behavioral psychology on ourselves.
Otherwise .. no.
Never feel bad about feelings you have.
But just because we feel some way does NOT mean it is always acceptable to ACT on this feelings.
Example .. ever heard someone say "I'm so mad I could KILL them!!!". That is a feeliing, and you can't just stop the feeling.
But to go and actually kill the person . .that is indeed very wrong.
So don't get upset about your feelings.
Keep them to yourself because you would only hurt your bf/gf if you told them.
And do not follow through on your feelings.
Understand that it takes a couple of years to adjust to someone and for the infatuation to die out. Then we face the challenge of learning to live without the excitement of the new relationship, and the struggle to learn how to be happy with life.
But this person we have feelings for . .our feelings about them are not based on them. Our feelings are based on our fantasy about them. And most likely we would not like them once our infatuation died out.
So don't take those feeling seriously.
Also, understand that the more you think about this other person, the stronger your HABIT of thinking about them will become. And the stronger it gets, the more you feel a compulsion TO pursue that other person.
So now is the time to decide .. are you going to move towards a future where you wreck your current relationship for someone who may or may not work out long-term .... or are you going to start turning your mind AWAY from dwelling on this other person, keeping your relationship and family intact.
It is your choice. But if you don't decide and take action to promote your decision, you may lose control and then you have no choice but to roll downhill like a car without brakes.